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class="breathe-horizontal" start="1"> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2411.00424">arXiv:2411.00424</a> <span> [<a href="https://arxiv.org/pdf/2411.00424">pdf</a>, <a href="https://arxiv.org/ps/2411.00424">ps</a>, <a href="https://arxiv.org/format/2411.00424">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.110.L101501">10.1103/PhysRevD.110.L101501 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Accreting Black Holes radiate classical Vaidya radiation to pave way for Hawking radiation </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Goswami%2C+R">Rituparno Goswami</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2411.00424v1-abstract-short" style="display: inline;"> It is well known that locally defined marginally outer trapped surface (MOTS) is null and coincident with the event horizon of an unperturbed static Schwarzschild black hole. This is however not true for an accreting black hole for which MOTS separates out and turns spacelike. In this letter, we obtain the necessary and sufficient condition for MOTS to remain null and coincident with the event hor… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2411.00424v1-abstract-full').style.display = 'inline'; document.getElementById('2411.00424v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2411.00424v1-abstract-full" style="display: none;"> It is well known that locally defined marginally outer trapped surface (MOTS) is null and coincident with the event horizon of an unperturbed static Schwarzschild black hole. This is however not true for an accreting black hole for which MOTS separates out and turns spacelike. In this letter, we obtain the necessary and sufficient condition for MOTS to remain null and coincident with the event horizon even when matter is continuously accreting on. This also has an important bearing on the quantum Hawking radiation which is supposed to emanate from the MOTS, and it cannot propagate out to infinity unless MOTS is null. The condition is, infalling timelike Type I fluid should turn null or Type II, as it falls on the horizon. This transition from timelike to null is caused by the tidal deformation of the infalling fluid, and that produces an outward directed heat flux giving rise to Vaidya radiation emanating out of the boundary of accreting zone. We thus predict a remarkable new phenomena that accreting black hole radiates classical Vaidya radiation that paves the way for the Hawking radiation. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2411.00424v1-abstract-full').style.display = 'none'; document.getElementById('2411.00424v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 1 November, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, Revtex4</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 110, L101501 (2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2404.06870">arXiv:2404.06870</a> <span> [<a href="https://arxiv.org/pdf/2404.06870">pdf</a>, <a href="https://arxiv.org/format/2404.06870">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Energetics of Buchdahl stars and the magnetic Penrose process </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Tursunov%2C+A">Arman Tursunov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2404.06870v2-abstract-short" style="display: inline;"> Buchdahl star is the most compact object without an event horizon and is an excellent candidate for a black hole mimicker. Unlike black holes, rotating Buchdahl star can be over-extremal with respect to the black hole, sustaining a larger spin. We show that it can also develop an ergosphere above the threshold spin $尾> 1/\sqrt{2}$, which allows extraction of its rotational energy. Electromagnetic… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.06870v2-abstract-full').style.display = 'inline'; document.getElementById('2404.06870v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2404.06870v2-abstract-full" style="display: none;"> Buchdahl star is the most compact object without an event horizon and is an excellent candidate for a black hole mimicker. Unlike black holes, rotating Buchdahl star can be over-extremal with respect to the black hole, sustaining a larger spin. We show that it can also develop an ergosphere above the threshold spin $尾> 1/\sqrt{2}$, which allows extraction of its rotational energy. Electromagnetic field around Buchdahl star is also expected to differ from that of black hole in both strength and topology. In this paper, we explore the energetics of Buchdahl star focusing on the magnetic Penrose process in the two magnetic field configurations, i.e., uniform and dipole. Below the threshold spin, Buchdahl star is expected to be quiet, while above the threshold it can be much more efficient than the black hole if a dipolar magnetic field is developed on its surface. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2404.06870v2-abstract-full').style.display = 'none'; document.getElementById('2404.06870v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 October, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 April, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, 4 captioned figures; discussions and references added</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C (2024) 84:1015 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2402.11503">arXiv:2402.11503</a> <span> [<a href="https://arxiv.org/pdf/2402.11503">pdf</a>, <a href="https://arxiv.org/format/2402.11503">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="History and Philosophy of Physics">physics.hist-ph</span> </div> </div> <p class="title is-5 mathjax"> C. V. Vishveshwara (Vishu) On The Black Hole Trek </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Nayak%2C+K+R">K Rajesh Nayak</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2402.11503v1-abstract-short" style="display: inline;"> With his seminal and pioneering work on the stability of the Schwarzschild black hole and its interaction with gravitational radiation, Vishu had opened a new window on black hole astrophysics. One of the interesting results that soon followed was that "a black hole has no hair", it is entirely specified by the three parameters, mass, spin and charge, and nothing more. The discovery of gravitation… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2402.11503v1-abstract-full').style.display = 'inline'; document.getElementById('2402.11503v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2402.11503v1-abstract-full" style="display: none;"> With his seminal and pioneering work on the stability of the Schwarzschild black hole and its interaction with gravitational radiation, Vishu had opened a new window on black hole astrophysics. One of the interesting results that soon followed was that "a black hole has no hair", it is entirely specified by the three parameters, mass, spin and charge, and nothing more. The discovery of gravitational waves in 2016 produced by merger of two black holes, and observed by the Ligo-Virgo collaboration, carried the definitive signature of quasi-normal modes, the phenomenon of black hole ringdown, exactly what Vishu had predicted in his 1970 Nature paper~(See Isaacson's commentary) 46 years ago. This was the crowning glory. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2402.11503v1-abstract-full').style.display = 'none'; document.getElementById('2402.11503v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 February, 2024; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> February 2024. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Resonance, Vol 29, P 11(2024) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2306.10872">arXiv:2306.10872</a> <span> [<a href="https://arxiv.org/pdf/2306.10872">pdf</a>, <a href="https://arxiv.org/format/2306.10872">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Gravitational Collapse in pure Gauss-Bonnet gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dialektopoulos%2C+K+F">Konstantinos F. Dialektopoulos</a>, <a href="/search/gr-qc?searchtype=author&query=Malafarina%2C+D">Daniele Malafarina</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2306.10872v1-abstract-short" style="display: inline;"> We study the process of gravitational collapse in pure Gauss-Bonnet gravity. In the homogeneous dust collapse, we show that the $D=7$ pure Gauss-Bonnet theory has gravitational dynamics indistinguishable from Einstein's theory in $D=4$, meaning that collapsing particle feel the same potential as in the classical 4-dimensional general relativistic case. In $D<7$ pure Gauss-Bonnet gravity becomes we… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.10872v1-abstract-full').style.display = 'inline'; document.getElementById('2306.10872v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2306.10872v1-abstract-full" style="display: none;"> We study the process of gravitational collapse in pure Gauss-Bonnet gravity. In the homogeneous dust collapse, we show that the $D=7$ pure Gauss-Bonnet theory has gravitational dynamics indistinguishable from Einstein's theory in $D=4$, meaning that collapsing particle feel the same potential as in the classical 4-dimensional general relativistic case. In $D<7$ pure Gauss-Bonnet gravity becomes weaker, while in $D>7$ it becomes stronger, with respect to General Relativity. In the inhomogeneous dust collapse we find the mass modes in the expansion of the energy density in any dimensions that lead to either naked singularities or black holes as final states of collapse. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2306.10872v1-abstract-full').style.display = 'none'; document.getElementById('2306.10872v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 19 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages, 10 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2304.10197">arXiv:2304.10197</a> <span> [<a href="https://arxiv.org/pdf/2304.10197">pdf</a>, <a href="https://arxiv.org/ps/2304.10197">ps</a>, <a href="https://arxiv.org/format/2304.10197">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> The Buchdahl Bound Denotes The Geometrical Virial Theorem </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Goswami%2C+R">Rituparno Goswami</a>, <a href="/search/gr-qc?searchtype=author&query=Hansraj%2C+C">Chevarra Hansraj</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2304.10197v2-abstract-short" style="display: inline;"> In this paper, we geometrically establish yet another correspondence between Newtonian mechanics and general relativity by connecting the Buchdahl bound and the Virial theorem. Buchdahl stars are defined by the saturation of the Buchdahl bound, $桅(R) \leq 4/9$ where $桅(R)$ is the gravitational potential felt by a radially falling particle. An interesting alternative characterization is given by gr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.10197v2-abstract-full').style.display = 'inline'; document.getElementById('2304.10197v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2304.10197v2-abstract-full" style="display: none;"> In this paper, we geometrically establish yet another correspondence between Newtonian mechanics and general relativity by connecting the Buchdahl bound and the Virial theorem. Buchdahl stars are defined by the saturation of the Buchdahl bound, $桅(R) \leq 4/9$ where $桅(R)$ is the gravitational potential felt by a radially falling particle. An interesting alternative characterization is given by gravitational energy being half of non-gravitational energy. With insightful identification of the former with kinetic and the latter with potential energy, it has been recently argued that the equilibrium of a Buchdahl star may be governed by the Virial theorem. In this paper, we provide a purely geometric version of this theorem and thereby of the Buchdahl star characterization. We show that the condition for an accreting Buchdahl star to remain in the state of Virial equilibrium is that it must expel energy via heat flux, appearing in the exterior as Vaidya radiation. If that happens then a Buchdahl star continues in the Virial equilibrium state without ever turning into a black hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2304.10197v2-abstract-full').style.display = 'none'; document.getElementById('2304.10197v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 June, 2024; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 20 April, 2023; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2023. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">15 pages</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2212.06745">arXiv:2212.06745</a> <span> [<a href="https://arxiv.org/pdf/2212.06745">pdf</a>, <a href="https://arxiv.org/ps/2212.06745">ps</a>, <a href="https://arxiv.org/format/2212.06745">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> On the equilibrium of the Buchdahl star </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2212.06745v4-abstract-short" style="display: inline;"> The Buchdahl star is the limiting compactness (which is indicated by sturation of the Buchdahl bound) object without horizon. It is in general defined by the potential felt by radially falling timelike particle, $桅(R) = 4/9$, in the field of a static object. On the other hand black hole is similarly characterized by $桅(R)=1/2$ which defines the horizon. Further it is remarkable that in terms of gr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2212.06745v4-abstract-full').style.display = 'inline'; document.getElementById('2212.06745v4-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2212.06745v4-abstract-full" style="display: none;"> The Buchdahl star is the limiting compactness (which is indicated by sturation of the Buchdahl bound) object without horizon. It is in general defined by the potential felt by radially falling timelike particle, $桅(R) = 4/9$, in the field of a static object. On the other hand black hole is similarly characterized by $桅(R)=1/2$ which defines the horizon. Further it is remarkable that in terms of gravitational and non-gravitational energy, the Buchdahl star is alternatively defined when gravitational energy is half of non-gravitational energy while the black hole when the two are equal. When an infinitely dispersed system of bare mass $M$ collapses under its own gravity to radius $R$, total energy encompassed inside $R$ would be $E_{tot}(R)=M-E_{grav}(R)$. That is, energy inside the object is increased by the amount equivalent to gravitational energy lying outside and which manifests as internal energy in the interior. If the interior consists of free particles in motion interacting only through gravity as is the case for the Vlasov kinetic matter, internal (gravitational) energy could be thought of as kinetic energy and the defining condition for the Buchdahl star would then be kinetic (gravitational) energy equal to half of non-gravitational (potential) energy. Consequently it could be envisaged that equilibrium of the Buchdahl star interior is governed by the celebrated Virial theorem like relation (average kinetic energy equal to half of average potential energy). On the same count the black hole equilibrium is governed by equality of gravitational and non-gravitational energy ! <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2212.06745v4-abstract-full').style.display = 'none'; document.getElementById('2212.06745v4-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 9 November, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 11 December, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, Title changed, abstract modified. Overall arguements and analysis revamped and sharpened. New references added. Main result remains unaltered</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.10153">arXiv:2209.10153</a> <span> [<a href="https://arxiv.org/pdf/2209.10153">pdf</a>, <a href="https://arxiv.org/format/2209.10153">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> Strong cosmic censorship conjecture for a charged AdS black hole </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Singha%2C+C">Chiranjeeb Singha</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.10153v2-abstract-short" style="display: inline;"> The strong cosmic censorship conjecture states (SCCC) that one cannot extend spacetime beyond the Cauchy horizon with a square-integrable connection. This conjecture was postulated to save the deterministic nature of the most successful theory of gravitation, general relativity. In order to explore the validation/violation of the SCCC for the charged anti-de Sitter black hole spacetime, we compute… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10153v2-abstract-full').style.display = 'inline'; document.getElementById('2209.10153v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.10153v2-abstract-full" style="display: none;"> The strong cosmic censorship conjecture states (SCCC) that one cannot extend spacetime beyond the Cauchy horizon with a square-integrable connection. This conjecture was postulated to save the deterministic nature of the most successful theory of gravitation, general relativity. In order to explore the validation/violation of the SCCC for the charged anti-de Sitter black hole spacetime, we compute the ratio of the imaginary part of the quasinormal mode frequencies and the surface gravity at the Cauchy horizon both analytically and numerically. The lowest value of which defines the key parameter $尾$ determining the fate of SCCC where $尾< 1/2$ indicates validation and else violation. We show that $尾> 1/2$ for a charged AdS black hole with the dissipative boundary conditions in the near extremal region. Thus the SCCC is violated for this spacetime. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.10153v2-abstract-full').style.display = 'none'; document.getElementById('2209.10153v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 21 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 1 figure</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2209.02560">arXiv:2209.02560</a> <span> [<a href="https://arxiv.org/pdf/2209.02560">pdf</a>, <a href="https://arxiv.org/format/2209.02560">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Like Black holes, Buchdahl stars cannot be extremalized </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2209.02560v2-abstract-short" style="display: inline;"> It was shown long back in \cite{Dadhich97} that a non-extremal black hole cannot be converted into an extremal one by test particle adiabatic accretion. The Buchdahl star is the most compact object without horizon and is defined by $桅(R) = 4/9$, while black hole by $桅(R) = 1/2$. Here $桅(R)$ is the gravitational potential experienced by a particle, radially falling for static and axially for the ro… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.02560v2-abstract-full').style.display = 'inline'; document.getElementById('2209.02560v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2209.02560v2-abstract-full" style="display: none;"> It was shown long back in \cite{Dadhich97} that a non-extremal black hole cannot be converted into an extremal one by test particle adiabatic accretion. The Buchdahl star is the most compact object without horizon and is defined by $桅(R) = 4/9$, while black hole by $桅(R) = 1/2$. Here $桅(R)$ is the gravitational potential experienced by a particle, radially falling for static and axially for the rotating object. In this short note we examine the question of extremalization of the Buchdhal star and show that the same result holds good as for the black hole. That is, a non-extremal Buchdahl star cannot be extremalized by test particle accretion. Further since extremal limit for BS is $>1$, it could facilitate formation of extremal black holes by neutral and spinless accretion. That is perhaps the only way they could be formed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2209.02560v2-abstract-full').style.display = 'none'; document.getElementById('2209.02560v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 6 October, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 6 September, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, 3 captioned figures. Accepted for publication in Phys. Lett. B</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2205.02231">arXiv:2205.02231</a> <span> [<a href="https://arxiv.org/pdf/2205.02231">pdf</a>, <a href="https://arxiv.org/ps/2205.02231">ps</a>, <a href="https://arxiv.org/format/2205.02231">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.105.124068">10.1103/PhysRevD.105.124068 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Novel way to the metric of higher dimensional rotating black holes </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dastgerdi%2C+A+A">Amin Aghababaie Dastgerdi</a>, <a href="/search/gr-qc?searchtype=author&query=Mirza%2C+B">Behrouz Mirza</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2205.02231v2-abstract-short" style="display: inline;"> We wish to carry forward to higher dimensions the insightful and novel method of obtaining the Kerr metric proposed by one of us [Gen. Relativ. Gravit. 45, 2383 (2013)] for deriving the Myers-Perry rotating black hole metric. We begin with a flat spacetime metric written in oblate spheroidal coordinates (ellipsoidal geometry) appropriate for the inclusion of rotation, and then introduce arbitrary… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.02231v2-abstract-full').style.display = 'inline'; document.getElementById('2205.02231v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2205.02231v2-abstract-full" style="display: none;"> We wish to carry forward to higher dimensions the insightful and novel method of obtaining the Kerr metric proposed by one of us [Gen. Relativ. Gravit. 45, 2383 (2013)] for deriving the Myers-Perry rotating black hole metric. We begin with a flat spacetime metric written in oblate spheroidal coordinates (ellipsoidal geometry) appropriate for the inclusion of rotation, and then introduce arbitrary functions to introduce a gravitational potential due to mass, which are then determined by requiring that a massless particle experiences no acceleration, while a massive particle feels Newtonian acceleration at large r. We further generalize the method to include the cosmological constant 螞 to obtain the MyersPerry de Sitter/antide Sitter black hole metric. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.02231v2-abstract-full').style.display = 'none'; document.getElementById('2205.02231v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 29 June, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 4 May, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Physical Review D 105, 124068 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2205.01350">arXiv:2205.01350</a> <span> [<a href="https://arxiv.org/pdf/2205.01350">pdf</a>, <a href="https://arxiv.org/ps/2205.01350">ps</a>, <a href="https://arxiv.org/format/2205.01350">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/1475-7516/2023/06/010">10.1088/1475-7516/2023/06/010 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Extending the weak cosmic censorship conjecture to the charged Buchdahl star by employing the gedanken experiments </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2205.01350v2-abstract-short" style="display: inline;"> In this paper, we wish to investigate the weak cosmic censorship conjecture (WCCC) for the non black hole object, Buchdahl star and test its validity. It turns out that the extremal limit for the star is over-extremal for black hole, $Q^2/M^2 \leq 9/8 >1$; i.e., it could have $9/8 \geq Q^2/M^2 > 1$. By carrying out both linear and non-linear perturbations, we establish the same result for the Buch… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.01350v2-abstract-full').style.display = 'inline'; document.getElementById('2205.01350v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2205.01350v2-abstract-full" style="display: none;"> In this paper, we wish to investigate the weak cosmic censorship conjecture (WCCC) for the non black hole object, Buchdahl star and test its validity. It turns out that the extremal limit for the star is over-extremal for black hole, $Q^2/M^2 \leq 9/8 >1$; i.e., it could have $9/8 \geq Q^2/M^2 > 1$. By carrying out both linear and non-linear perturbations, we establish the same result for the Buchdahl star as well. That is, as for black hole it could be overcharged at the linear perturbation while the result is overturned when the non-linear perturbations are included. Thus WCCC is always obeyed by the Buchdahl star. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.01350v2-abstract-full').style.display = 'none'; document.getElementById('2205.01350v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 11 June, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 3 May, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">17 pages, no figures. Updated to match with the published version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> JCAP 06 (2023) 010 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2205.00875">arXiv:2205.00875</a> <span> [<a href="https://arxiv.org/pdf/2205.00875">pdf</a>, <a href="https://arxiv.org/ps/2205.00875">ps</a>, <a href="https://arxiv.org/format/2205.00875">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s10714-022-02967-8">10.1007/s10714-022-02967-8 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Fundamental forces and their dynamics </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2205.00875v2-abstract-short" style="display: inline;"> In this essay, we wish to propose a general principle: \it{the equation of motion or dynamics of a fundamental force should not be prescribed but instead be entirely driven by geometry of the appropriate spacetime manifold, and the equation is then obtained by employing only the geometric property without appeal to an action.} The motivation for this pronouncement comes from the fact that the equa… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.00875v2-abstract-full').style.display = 'inline'; document.getElementById('2205.00875v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2205.00875v2-abstract-full" style="display: none;"> In this essay, we wish to propose a general principle: \it{the equation of motion or dynamics of a fundamental force should not be prescribed but instead be entirely driven by geometry of the appropriate spacetime manifold, and the equation is then obtained by employing only the geometric property without appeal to an action.} The motivation for this pronouncement comes from the fact that the equation of motion of general relativity follows from the geometry of Riemannian spacetime manifold without appeal to anything else from outside. The driving differential geometric property is the Bianchi identity satisfied by the Riemann curvature tensor. Similarly it is geometry of the principal tangent bundle of fibre spacetime manifold that may account for dynamics of the gauge vector fields. It is the classical electric force for the Abelian gauge symmetry group while the non-Abelian symmetry leads to the non-Abelian forces, the weak and the strong. We shall also reflect on a unified picture of the basic forces, and the duality correspondences it may inspire. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2205.00875v2-abstract-full').style.display = 'none'; document.getElementById('2205.00875v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 August, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 29 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Revamped and published version, Contribution to Professor T. Padmanabhan memorial volume, GRG Journal</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Gen. Relativ. Grav. \{bf 54}, 83 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2204.10734">arXiv:2204.10734</a> <span> [<a href="https://arxiv.org/pdf/2204.10734">pdf</a>, <a href="https://arxiv.org/format/2204.10734">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-023-11793-4">10.1140/epjc/s10052-023-11793-4 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Universality of the Buchdahl sphere </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2204.10734v2-abstract-short" style="display: inline;"> Buchdahl sphere, the limiting stable isotropic stellar structure without exotic matter, plays a very important role in our understanding of how compact an astrophysical object can be. Here, we show certain universal properties associated with the Buchdahl sphere, in the sense that these properties will not change with the inclusion of electric charge in the stellar structure, or, will hold good in… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.10734v2-abstract-full').style.display = 'inline'; document.getElementById('2204.10734v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2204.10734v2-abstract-full" style="display: none;"> Buchdahl sphere, the limiting stable isotropic stellar structure without exotic matter, plays a very important role in our understanding of how compact an astrophysical object can be. Here, we show certain universal properties associated with the Buchdahl sphere, in the sense that these properties will not change with the inclusion of electric charge in the stellar structure, or, will hold good in the pure Lovelock theories of gravity as well. Using these universalities, we have proposed a Buchdahl limit for a slowly-rotating stellar configuration, for the first time. Finally, the universality of the Buchdahl sphere in terms of the gravitational and non-gravitational field energies, as well as for the photon sphere have also been discussed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2204.10734v2-abstract-full').style.display = 'none'; document.getElementById('2204.10734v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 18 August, 2023; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Published version, 20 pages, 2 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C 83, 677 (2023) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2203.07708">arXiv:2203.07708</a> <span> [<a href="https://arxiv.org/pdf/2203.07708">pdf</a>, <a href="https://arxiv.org/format/2203.07708">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/JHEP06(2022)028">10.1007/JHEP06(2022)028 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Strong cosmic censorship conjecture for a charged BTZ black hole </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Singha%2C+C">Chiranjeeb Singha</a>, <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2203.07708v3-abstract-short" style="display: inline;"> The strong cosmic censorship conjecture, whose validation asserts the deterministic nature of general relativity, has been studied for charged BTZ black holes in three dimensional general relativity, as well as for Nth order pure Lovelock gravity in d=2N+1 spacetime dimensions. Through both analytical and numerical routes, we have computed the ratio of the imaginary part of the quasi-normal mode f… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.07708v3-abstract-full').style.display = 'inline'; document.getElementById('2203.07708v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2203.07708v3-abstract-full" style="display: none;"> The strong cosmic censorship conjecture, whose validation asserts the deterministic nature of general relativity, has been studied for charged BTZ black holes in three dimensional general relativity, as well as for Nth order pure Lovelock gravity in d=2N+1 spacetime dimensions. Through both analytical and numerical routes, we have computed the ratio of the imaginary part of the quasi-normal mode frequencies with the surface gravity at the Cauchy horizon. The lowest of which corresponds to the key parameter associated with violation of strong cosmic censorship conjecture. Our results demonstrate that this parameter is always less than the critical value $(1/2)$, thereby respecting the strong cosmic censorship conjecture. This is in complete contrast to the four or, higher dimensional black holes, as well as for rotating BTZ black hole, where the violation of strong cosmic censorship conjecture exists. Implications and possible connection with the stability of the photon orbits have been discussed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2203.07708v3-abstract-full').style.display = 'none'; document.getElementById('2203.07708v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 June, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 March, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">20 pages, 6 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> JHEP06(2022)028 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2201.10381">arXiv:2201.10381</a> <span> [<a href="https://arxiv.org/pdf/2201.10381">pdf</a>, <a href="https://arxiv.org/ps/2201.10381">ps</a>, <a href="https://arxiv.org/format/2201.10381">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.105.064044">10.1103/PhysRevD.105.064044 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Maximum Force for Black Holes and Buchdahl Stars </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2201.10381v2-abstract-short" style="display: inline;"> Black hole and Buchdahl star are identified respectively by $桅(R)=1/2, 4/9$ where $g_{tt}=1-2桅(R)$ for a spherically symmetric static metric. We investigate the maximum force for black hole and Buchdahl star when one of the participating objects is charged and/or rotating while the other is neutral and non-rotating. It turns out that the maximum force between two Schwarzschild objects is universal… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2201.10381v2-abstract-full').style.display = 'inline'; document.getElementById('2201.10381v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2201.10381v2-abstract-full" style="display: none;"> Black hole and Buchdahl star are identified respectively by $桅(R)=1/2, 4/9$ where $g_{tt}=1-2桅(R)$ for a spherically symmetric static metric. We investigate the maximum force for black hole and Buchdahl star when one of the participating objects is charged and/or rotating while the other is neutral and non-rotating. It turns out that the maximum force between two Schwarzschild objects is universal, given in terms of the fundamental constant velocity of light and the gravitational constant in general relativity (GR) in the usual four dimensional spacetime. In general this feature uniquely picks out the pure Lovelock gravity (having only one $N$th order term in action which includes GR in the linear order $N=1$) and the dimensional spectrum, $D=3N+1$, where $N$ is degree of the Lovelock polynomial action. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2201.10381v2-abstract-full').style.display = 'none'; document.getElementById('2201.10381v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 28 February, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 24 January, 2022; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2022. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, Abstract is revamped, some references are added and the CAS grant his acknowledged. No change in the results. Accepted for publication in PRD</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. {\bf D105}, 0640044 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2104.00427">arXiv:2104.00427</a> <span> [<a href="https://arxiv.org/pdf/2104.00427">pdf</a>, <a href="https://arxiv.org/format/2104.00427">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Circular orbits around higher dimensional Einstein and pure Gauss-Bonnet rotating black holes </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2104.00427v3-abstract-short" style="display: inline;"> In this paper we study circular orbits around higher dimensional rotating Myers-Perry and pure Gauss-Bonnet (GB) black holes. It turns out that for the former there occurs no potential well to harbour bound and thereby stable circular orbits. The only circular orbits that could occur are all unstable and their radius is bounded from the below by that of the photon circular orbit. On the other hand… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2104.00427v3-abstract-full').style.display = 'inline'; document.getElementById('2104.00427v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2104.00427v3-abstract-full" style="display: none;"> In this paper we study circular orbits around higher dimensional rotating Myers-Perry and pure Gauss-Bonnet (GB) black holes. It turns out that for the former there occurs no potential well to harbour bound and thereby stable circular orbits. The only circular orbits that could occur are all unstable and their radius is bounded from the below by that of the photon circular orbit. On the other hand bound and stable circular orbits do exist for pure GB/Lovelock rotating black holes (the metric is though not an exact solution of pure Lovelock vacuum equation but it satisfies the equation in the leading order and has all the desired properties) in dimensions, $2N+2 \leq D \leq 4N$ (for $N=2$ pure GB in $D = 6, 7, 8$) where $N$ is the degree of Lovelock polynomial. Thus bound and stable circular orbits could exist around higher dimensional rotating black holes only for pure GB/Lovelock gravity. This property is a nice discriminator between Myers-Perry and pure GB/Lovelock rotating black holes. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2104.00427v3-abstract-full').style.display = 'none'; document.getElementById('2104.00427v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 1 April, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">16 pages, 13 figures, 2 tables</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Physics of the Dark Universe 35, 100986 (2022) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2101.02958">arXiv:2101.02958</a> <span> [<a href="https://arxiv.org/pdf/2101.02958">pdf</a>, <a href="https://arxiv.org/format/2101.02958">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-022-10256-6">10.1140/epjc/s10052-022-10256-6 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Pure Gauss-Bonnet NUT Black Hole Solution: I </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Mukherjee%2C+S">Sajal Mukherjee</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2101.02958v2-abstract-short" style="display: inline;"> We find a new exact $螞$-vacuum solution in pure Gauss-Bonnet gravity with NUT charge in six dimension with horizon having product topology $S^{(2)} \times S^{(2)}$. We also discuss its horizon and singularity structure, and consequently arrive at a parameter window for its physical viability. It should be noted that all NUT black hole solutions in higher dimensions have product, instead of spheric… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.02958v2-abstract-full').style.display = 'inline'; document.getElementById('2101.02958v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2101.02958v2-abstract-full" style="display: none;"> We find a new exact $螞$-vacuum solution in pure Gauss-Bonnet gravity with NUT charge in six dimension with horizon having product topology $S^{(2)} \times S^{(2)}$. We also discuss its horizon and singularity structure, and consequently arrive at a parameter window for its physical viability. It should be noted that all NUT black hole solutions in higher dimensions have product, instead of spherical, topology. We prove, in general, that it is because of the radial symmetry of the NUT spacetime; i.e. in higher dimensions NUT spacetime cannot maintain radial symmetry unless horizon has $S^{(2)}$ or its product topology. On the way we also prove a general result for spherical symmetry that when null energy condition is satisfied, one has then only to solve a first order equation to get a vacuum or $螞$-vacuum solution. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2101.02958v2-abstract-full').style.display = 'none'; document.getElementById('2101.02958v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 April, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 8 January, 2021; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> January 2021. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">19 pages, 5 figures, Published in: Eur.Phys.J.C</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2012.15560">arXiv:2012.15560</a> <span> [<a href="https://arxiv.org/pdf/2012.15560">pdf</a>, <a href="https://arxiv.org/format/2012.15560">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-021-09242-1">10.1140/epjc/s10052-021-09242-1 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Pure Gauss-Bonnet NUT black hole with and without non-central singularity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Mukherjee%2C+S">Sajal Mukherjee</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2012.15560v2-abstract-short" style="display: inline;"> It is known that NUT solution has many interesting features and pathologies like being non-singular and having closed timelike curves. It turns out that in higher dimensions horizon topology cannot be spherical but it has instead to be product of $2$-spheres so as to retain radial symmetry of spacetime. In this letter we wish to present a new solution of pure Gauss-Bonnet $螞$-vacuum equation descr… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.15560v2-abstract-full').style.display = 'inline'; document.getElementById('2012.15560v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2012.15560v2-abstract-full" style="display: none;"> It is known that NUT solution has many interesting features and pathologies like being non-singular and having closed timelike curves. It turns out that in higher dimensions horizon topology cannot be spherical but it has instead to be product of $2$-spheres so as to retain radial symmetry of spacetime. In this letter we wish to present a new solution of pure Gauss-Bonnet $螞$-vacuum equation describing a black hole with NUT charge. It has three interesting cases: (a) black hole with both event and cosmological horizons with singularity being hidden behind the former, (b) a regular spacetime free of both horizon and singularity, and (c) black hole with event horizon without singularity and cosmological horizon. Singularity here is always non-centric at $r \neq 0$. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2012.15560v2-abstract-full').style.display = 'none'; document.getElementById('2012.15560v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 June, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 31 December, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> December 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">4 pages, 3 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C 81, 458 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2009.10528">arXiv:2009.10528</a> <span> [<a href="https://arxiv.org/pdf/2009.10528">pdf</a>, <a href="https://arxiv.org/format/2009.10528">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> On black hole formation in higher dimensions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2009.10528v4-abstract-short" style="display: inline;"> The two main processes of black hole formation are: one, collapse of a matter cloud under its own gravity and the other is accretion of matter onto an already existing gravitating centre. The necessary condition for both the processes to operate is that overall force on collapsing fluid element or on test accreting particles is attractive. It turns out that this is not the case in general in highe… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.10528v4-abstract-full').style.display = 'inline'; document.getElementById('2009.10528v4-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2009.10528v4-abstract-full" style="display: none;"> The two main processes of black hole formation are: one, collapse of a matter cloud under its own gravity and the other is accretion of matter onto an already existing gravitating centre. The necessary condition for both the processes to operate is that overall force on collapsing fluid element or on test accreting particles is attractive. It turns out that this is not the case in general in higher dimensions greater than the usual four for collapsing or accreting matter having non-zero angular momentum. Thus both these processes cannot operate in higher dimensions to form a rotating black hole. The only theory in which this is not the case in higher dimensions is the pure Lovelock gravity where both these processes could in principle work for formation of black holes. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2009.10528v4-abstract-full').style.display = 'none'; document.getElementById('2009.10528v4-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 27 October, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, one figure; Accepted for publication in IJMPD. Updated to match the accepted version</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2008.04092">arXiv:2008.04092</a> <span> [<a href="https://arxiv.org/pdf/2008.04092">pdf</a>, <a href="https://arxiv.org/format/2008.04092">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> Weak cosmic censorship conjecture in the pure Lovelock gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2008.04092v2-abstract-short" style="display: inline;"> It is well known that a rotating black hole in four dimension could be overspun by linear order test particle accretion which however always gets overturned when non-linear perturbations are included. It turns out that in the Einstein gravity, repulsion due to rotation dominates over attraction due to mass in dimensions, $D>5$, and consequently black hole cannot be overspun even for linear order a… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.04092v2-abstract-full').style.display = 'inline'; document.getElementById('2008.04092v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2008.04092v2-abstract-full" style="display: none;"> It is well known that a rotating black hole in four dimension could be overspun by linear order test particle accretion which however always gets overturned when non-linear perturbations are included. It turns out that in the Einstein gravity, repulsion due to rotation dominates over attraction due to mass in dimensions, $D>5$, and consequently black hole cannot be overspun even for linear order accretion. For the pure Lovelock rotating black hole, this dimensional threshold is $D>4N+1$ where $N$ is degree of single $N$th order term in the Lovelock polynomial in the action. Thus the pure Lovelock rotating black holes always obey the weak cosmic censorship conjecture (WCCC) in all dimensions greater than $4N+1$. Since overall gravity being repulsive beyond this dimensional threshold, how is rotating black hole then formed there? <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2008.04092v2-abstract-full').style.display = 'none'; document.getElementById('2008.04092v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 August, 2022; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 10 August, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 1 captioned figure</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2006.10561">arXiv:2006.10561</a> <span> [<a href="https://arxiv.org/pdf/2006.10561">pdf</a>, <a href="https://arxiv.org/format/2006.10561">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-021-08894-3">10.1140/epjc/s10052-021-08894-3 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> An electromagnetic extension of the Schwarzschild interior solution and the corresponding Buchdahl limit </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Sharma%2C+R">Ranjan Sharma</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Das%2C+S">Shyam Das</a>, <a href="/search/gr-qc?searchtype=author&query=Maharaj%2C+S+D">Sunil D. Maharaj</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2006.10561v1-abstract-short" style="display: inline;"> We wish to construct a model for charged star as a generalization of the uniform density Schwarzschild interior solution. We employ the Vaidya and Tikekar ansatz [{\it Astrophys. Astron.} {\bf 3} (1982) 325] for one of the metric potentials and electric field is chosen in such a way that when it is switched off the metric reduces to the Schwarzschild. This relates charge distribution to the Vaidya… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2006.10561v1-abstract-full').style.display = 'inline'; document.getElementById('2006.10561v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2006.10561v1-abstract-full" style="display: none;"> We wish to construct a model for charged star as a generalization of the uniform density Schwarzschild interior solution. We employ the Vaidya and Tikekar ansatz [{\it Astrophys. Astron.} {\bf 3} (1982) 325] for one of the metric potentials and electric field is chosen in such a way that when it is switched off the metric reduces to the Schwarzschild. This relates charge distribution to the Vaidya-Tikekar parameter, $k$, indicating deviation form sphericity of three dimensional space when embedded into four dimensional Euclidean space. The model is examined against all the physical conditions required for a relativistic charged fluid sphere as an interior to a charged star. We also obtain and discuss charged analogue of the Buchdahl compactness bound. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2006.10561v1-abstract-full').style.display = 'none'; document.getElementById('2006.10561v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 June, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 8 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2006.07338">arXiv:2006.07338</a> <span> [<a href="https://arxiv.org/pdf/2006.07338">pdf</a>, <a href="https://arxiv.org/ps/2006.07338">ps</a>, <a href="https://arxiv.org/format/2006.07338">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.102.064018">10.1103/PhysRevD.102.064018 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Maximum Force in Modified Gravity Theories </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Barrow%2C+J+D">John D. Barrow</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2006.07338v3-abstract-short" style="display: inline;"> We investigate the existence and nature of classical maximum force bound between two black holes with touching horizons. Besides general relativity, the maximum force bound is independent of black hole masses only in Moffat's theory, Brans Dicke theory (which is the same as Einstein's for vacuum) and the higher dimensional generalization of Einstein's theory, pure Lovelock gravity which is charact… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2006.07338v3-abstract-full').style.display = 'inline'; document.getElementById('2006.07338v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2006.07338v3-abstract-full" style="display: none;"> We investigate the existence and nature of classical maximum force bound between two black holes with touching horizons. Besides general relativity, the maximum force bound is independent of black hole masses only in Moffat's theory, Brans Dicke theory (which is the same as Einstein's for vacuum) and the higher dimensional generalization of Einstein's theory, pure Lovelock gravity which is characterised by having single $n$th order term in Lovelock polynomial without sum over lower orders in the action. Further if the bound is to exist in higher dimensions and is entirely in terms of the velocity of light and the gravitational constant, it has uniquely to be pure Lovelock gravity. In pure Lovelock gravity, the maximum force bound exists in all $3n$-space dimensions and has the value, $c^4/4G_n$ where $G_n$ is the corresponding gravitational constant. The absence of mass dependence in the maximum force bound may have relevance for the formation of naked singularities. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2006.07338v3-abstract-full').style.display = 'none'; document.getElementById('2006.07338v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 28 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 12 June, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, no figures, section on power law gravity dropped, additions to conclusions, The paper is dedicated to the fond memory of one of the authors, John Barrow who passed away on 26 Sept 2020 - Naresh Dadhich, coauthor</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 102, 064018 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2005.07504">arXiv:2005.07504</a> <span> [<a href="https://arxiv.org/pdf/2005.07504">pdf</a>, <a href="https://arxiv.org/format/2005.07504">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1016/j.dark.2020.100658">10.1016/j.dark.2020.100658 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Limits on stellar structures in Lovelock theories of gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2005.07504v2-abstract-short" style="display: inline;"> We study the bound on the compactness of a stellar object in pure Lovelock theories of arbitrary order in arbitrary spacetime dimensions, involving electromagnetic field. The bound we derive for a generic pure Lovelock theory, reproduces the known results in four dimensional Einstein gravity. Both the case of a charged shell and that of a charge sphere demonstrates that for a given spacetime dimen… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.07504v2-abstract-full').style.display = 'inline'; document.getElementById('2005.07504v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2005.07504v2-abstract-full" style="display: none;"> We study the bound on the compactness of a stellar object in pure Lovelock theories of arbitrary order in arbitrary spacetime dimensions, involving electromagnetic field. The bound we derive for a generic pure Lovelock theory, reproduces the known results in four dimensional Einstein gravity. Both the case of a charged shell and that of a charge sphere demonstrates that for a given spacetime dimension, stars in general relativity are more compact than the stars in pure Lovelock theories. In addition, as the strength of the Maxwell field increases, the stellar structures become more compact, i.e., the radius of the star decreases. In the context of four dimensional Einstein-Gauss-Bonnet gravity as well, an increase in the strength of the Gauss-Bonnet coupling (behaving as an effective electric charge), increases the compactness of the star. Implications are discussed. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.07504v2-abstract-full').style.display = 'none'; document.getElementById('2005.07504v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 July, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 May, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">v2, minor revision, published version, 36 pages, 7 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Dark Univ. 30, 100658 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2005.05757">arXiv:2005.05757</a> <span> [<a href="https://arxiv.org/pdf/2005.05757">pdf</a>, <a href="https://arxiv.org/ps/2005.05757">ps</a>, <a href="https://arxiv.org/format/2005.05757">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> On causal structure of $4D$-Einstein-Gauss-Bonnet black hole </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2005.05757v3-abstract-short" style="display: inline;"> The recently proposed effective equation of motion for the $4D$- Einstein-Gauss-Bonnet gravity admits a static black hole solution that has, like the Rissner-Nordstr枚m charged black hole, two horizons instead of one for the Schwarzschild black hole. This means that the central singularity is timelike instead of spacelike. It should though be noted that in $D\geq5$, the solution always admits only… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.05757v3-abstract-full').style.display = 'inline'; document.getElementById('2005.05757v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2005.05757v3-abstract-full" style="display: none;"> The recently proposed effective equation of motion for the $4D$- Einstein-Gauss-Bonnet gravity admits a static black hole solution that has, like the Rissner-Nordstr枚m charged black hole, two horizons instead of one for the Schwarzschild black hole. This means that the central singularity is timelike instead of spacelike. It should though be noted that in $D\geq5$, the solution always admits only one horizon like the Schwarzshild solution. In the equation defining the horizon, the rescaled Gauss-Bonnet coupling constant appears as a new 'gravitational charge' with a repulsive effect to cause in addition to event horizon a Cauchy horizon. Thus it radically alters the causal structure of the black hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2005.05757v3-abstract-full').style.display = 'none'; document.getElementById('2005.05757v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 10 September, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 11 May, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">4 pages, no figures, References added, matches with the published version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. {\bf C80}, 832 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2004.09242">arXiv:2004.09242</a> <span> [<a href="https://arxiv.org/pdf/2004.09242">pdf</a>, <a href="https://arxiv.org/format/2004.09242">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1016/j.dark.2020.100758">10.1016/j.dark.2020.100758 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> On overspinning of black holes in higher dimensions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2004.09242v2-abstract-short" style="display: inline;"> It turns out that repulsive effect due to rotation of a rotating black hole dominates over attraction due to mass for large $r$ in dimensions $>5$. This gives rise to a remarkable result that black hole in these higher dimensions in contrast to lower dimensional ones cannot be overspun even under linear test particle accretion. Further if a black hole in dimension $>4$ has one of its rotation para… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.09242v2-abstract-full').style.display = 'inline'; document.getElementById('2004.09242v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2004.09242v2-abstract-full" style="display: none;"> It turns out that repulsive effect due to rotation of a rotating black hole dominates over attraction due to mass for large $r$ in dimensions $>5$. This gives rise to a remarkable result that black hole in these higher dimensions in contrast to lower dimensional ones cannot be overspun even under linear test particle accretion. Further if a black hole in dimension $>4$ has one of its rotation parameters zero, it has only one horizon and hence it can never be overspun. Thus rotating black holes in six and higher dimensions, and those with one rotation parameter switched off, would always obey the weak cosmic censorship conjecture (WCCC). <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.09242v2-abstract-full').style.display = 'none'; document.getElementById('2004.09242v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 5 January, 2021; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 20 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, 2 figures; references added, minor changes made</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Physics of the Dark Universe 31, 100758 (2021) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2004.07907">arXiv:2004.07907</a> <span> [<a href="https://arxiv.org/pdf/2004.07907">pdf</a>, <a href="https://arxiv.org/format/2004.07907">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3847/1538-4357/ab8ae9">10.3847/1538-4357/ab8ae9 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Supermassive black holes as possible sources of ultra high energy cosmic rays </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Tursunov%2C+A">Arman Tursunov</a>, <a href="/search/gr-qc?searchtype=author&query=Stuchl%C3%ADk%2C+Z">Zden臎k Stuchl铆k</a>, <a href="/search/gr-qc?searchtype=author&query=Kolo%C5%A1%2C+M">Martin Kolo拧</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2004.07907v2-abstract-short" style="display: inline;"> Production and acceleration mechanisms of ultra-high-energy cosmic rays (UHECRs) of energy $>10^{20}$eV, clearly beyond the GZK-cutoff limit remain unclear that points to exotic nature of the phenomena. Recent observations of extragalactic neutrino may indicate the source of UHECRs being an extragalactic supermassive black hole (SMBH). We demonstrate that ultra-efficient energy extraction from rot… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07907v2-abstract-full').style.display = 'inline'; document.getElementById('2004.07907v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2004.07907v2-abstract-full" style="display: none;"> Production and acceleration mechanisms of ultra-high-energy cosmic rays (UHECRs) of energy $>10^{20}$eV, clearly beyond the GZK-cutoff limit remain unclear that points to exotic nature of the phenomena. Recent observations of extragalactic neutrino may indicate the source of UHECRs being an extragalactic supermassive black hole (SMBH). We demonstrate that ultra-efficient energy extraction from rotating SMBH driven by the magnetic Penrose process (MPP) could indeed foot the bill. We envision ionization of neutral particles, such as neutron beta-decay, skirting close to the black hole horizon that energizes protons to over $10^{20}$eV for SMBH of mass $10^9 M_{\odot}$ and magnetic field of strength $10^4$G. Applied to Galactic center SMBH we have proton energy of order $\approx 10^{15.6}$eV that coincides with the knee of the cosmic ray spectra. We show that large $纬_z$ factors of high-energy particles along the escaping directions occur only in the presence of induced charge of the black hole that is known as the Wald charge in the case of uniform magnetic field. It is remarkable that the process neither requires extended acceleration zone, nor fine-tuning of accreting matter parameters. Further, this leads to certain verifiable constraints on SMBH's mass and magnetic field strength as UHECRs sources. This clearly makes ultra-efficient regime of MPP one of the most promising mechanisms for fueling UHECRs powerhouse. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07907v2-abstract-full').style.display = 'none'; document.getElementById('2004.07907v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 24 May, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 16 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">14 pages, 6 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> ApJ 895, 14 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/2004.07089">arXiv:2004.07089</a> <span> [<a href="https://arxiv.org/pdf/2004.07089">pdf</a>, <a href="https://arxiv.org/ps/2004.07089">ps</a>, <a href="https://arxiv.org/format/2004.07089">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1016/j.dark.2020.100598">10.1016/j.dark.2020.100598 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Dust collapse in 4D Einstein-Gauss-Bonnet gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Malafarina%2C+D">Daniele Malafarina</a>, <a href="/search/gr-qc?searchtype=author&query=Toshmatov%2C+B">Bobir Toshmatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="2004.07089v2-abstract-short" style="display: inline;"> We consider gravitational collapse in the recently proposed 4D limit of Einstein-Gauss-Bonnet gravity. We show that for collapse of a sphere made of homogeneous dust the process is qualitatively similar to the case of pure Einstein's gravity. The singularity forms as the endstate of collapse and it is trapped behind the horizon at all times. However, and differently from Einstein's theory, as a co… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07089v2-abstract-full').style.display = 'inline'; document.getElementById('2004.07089v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="2004.07089v2-abstract-full" style="display: none;"> We consider gravitational collapse in the recently proposed 4D limit of Einstein-Gauss-Bonnet gravity. We show that for collapse of a sphere made of homogeneous dust the process is qualitatively similar to the case of pure Einstein's gravity. The singularity forms as the endstate of collapse and it is trapped behind the horizon at all times. However, and differently from Einstein's theory, as a consequence of the Gauss-Bonnet term, the collapsing cloud reaches the singularity with zero velocity, and the time of formation of the singularity is delayed with respect to the pure Einstein case. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('2004.07089v2-abstract-full').style.display = 'none'; document.getElementById('2004.07089v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 30 May, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 15 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2020. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, 3 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Physics of the Dark Universe 30 (2020) 100598 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1908.07799">arXiv:1908.07799</a> <span> [<a href="https://arxiv.org/pdf/1908.07799">pdf</a>, <a href="https://arxiv.org/ps/1908.07799">ps</a>, <a href="https://arxiv.org/format/1908.07799">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.101.044028">10.1103/PhysRevD.101.044028 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Six-dimensional Myers-Perry rotating black hole cannot be overspun </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1908.07799v2-abstract-short" style="display: inline;"> Though under nonlinear accretion, all black holes in four and higher dimensions obey the weak cosmic censorship conjecture (CCC); however, they generally violate it for linear test particle accretion with the exception of five-dimensional rotating black hole with a single rotation. In dimensions greater than five, there exists no extremal condition for black hole with single rotation and hence it… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.07799v2-abstract-full').style.display = 'inline'; document.getElementById('1908.07799v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1908.07799v2-abstract-full" style="display: none;"> Though under nonlinear accretion, all black holes in four and higher dimensions obey the weak cosmic censorship conjecture (CCC); however, they generally violate it for linear test particle accretion with the exception of five-dimensional rotating black hole with a single rotation. In dimensions greater than five, there exists no extremal condition for black hole with single rotation and hence it can never be overspun. However, the extremal condition does exist for five-dimensional black hole with two rotations and then it could indeed be overspun under linear accretion. In this paper, we study the case of six-dimensional rotating black hole with two rotations and show that unlike the five-dimensional black hole it cannot be overspun under linear accretion. Though for nonlinear accretion, this result is anyway expected to hold good, yet we have verified it with an explicit calculation. Further, we would like to conjecture that so should be the case in all dimensions greater than six. Thus, the weak CCC may always be obeyed even at linear accretion process for rotating black hole in all dimensions greater than five. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.07799v2-abstract-full').style.display = 'none'; document.getElementById('1908.07799v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 February, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 21 August, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, no figures, 1 Table</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 101, 044028 (2020) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1908.01195">arXiv:1908.01195</a> <span> [<a href="https://arxiv.org/pdf/1908.01195">pdf</a>, <a href="https://arxiv.org/format/1908.01195">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-020-8009-4">10.1140/epjc/s10052-020-8009-4 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Five dimensional charged rotating minimally gauged supergravity black hole cannot be over-spun and/or over-charged in non-linear accretion </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a>, <a href="/search/gr-qc?searchtype=author&query=Jamil%2C+M">Mubasher Jamil</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1908.01195v3-abstract-short" style="display: inline;"> Generally black hole could be over charged/spun violating the weak cosmic censorship conjecture (WCCC) for linear order accretion while the same is always restored back for non-linear accretion. The only exception however is that of a five dimensional rotating black hole with single rotation that cannot be overspun even at linear order. In this paper we investigate this question for a five dimensi… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.01195v3-abstract-full').style.display = 'inline'; document.getElementById('1908.01195v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1908.01195v3-abstract-full" style="display: none;"> Generally black hole could be over charged/spun violating the weak cosmic censorship conjecture (WCCC) for linear order accretion while the same is always restored back for non-linear accretion. The only exception however is that of a five dimensional rotating black hole with single rotation that cannot be overspun even at linear order. In this paper we investigate this question for a five dimensional charged rotating minimally gauged supergravity black hole and show that it could not be overspun under non-linear accretion and thereby respecting WCCC. However in the case of single rotation WCCC is however also respected for linear accretion when angular momentum of accreting particle is greater than its charge irrespective of relative dominance of charge and rotation parameters of black hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1908.01195v3-abstract-full').style.display = 'none'; document.getElementById('1908.01195v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 25 May, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 3 August, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">12 pages, 2 figures; accepted for publication in Eur. Phys. J. C. Figures and further references have been added</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C (2020) 80:481 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1907.09503">arXiv:1907.09503</a> <span> [<a href="https://arxiv.org/pdf/1907.09503">pdf</a>, <a href="https://arxiv.org/ps/1907.09503">ps</a>, <a href="https://arxiv.org/format/1907.09503">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.100.084011">10.1103/PhysRevD.100.084011 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Pure Lovelock black hole in the dimension, $d=3N+1$, is stable </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Gannouji%2C+R">Radouane Gannouji</a>, <a href="/search/gr-qc?searchtype=author&query=Baez%2C+Y+R">Yolbeiker Rodr铆guez Baez</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1907.09503v2-abstract-short" style="display: inline;"> In this paper we show that pure Lovelock static Schwarzschild's analogue black hole in dimensions $d>3N+1$, where $N$ is the degree of Lovelock polynomial action, is stable even though pure Gauss-Bonnet $N=2$ black hole is unstable in dimension $d<7$. We also discuss and compare quasinormal modes for pure Lovelock and the corresponding Einstein black hole in the same dimension. We find that pertur… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1907.09503v2-abstract-full').style.display = 'inline'; document.getElementById('1907.09503v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1907.09503v2-abstract-full" style="display: none;"> In this paper we show that pure Lovelock static Schwarzschild's analogue black hole in dimensions $d>3N+1$, where $N$ is the degree of Lovelock polynomial action, is stable even though pure Gauss-Bonnet $N=2$ black hole is unstable in dimension $d<7$. We also discuss and compare quasinormal modes for pure Lovelock and the corresponding Einstein black hole in the same dimension. We find that perturbations decay with characteristic time which is weakly dimensional dependent as it depends only on the gravitational potential of the background solution, while frequency of oscillations however depend on the dimension. Also we show that spectrum of perturbations is not isospectral except in $d=4$. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1907.09503v2-abstract-full').style.display = 'none'; document.getElementById('1907.09503v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 12 September, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 22 July, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">7 pages, 4 figures, v2 accepted for publication in PRD, conclusions unchanged</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 100, 084011 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1905.05321">arXiv:1905.05321</a> <span> [<a href="https://arxiv.org/pdf/1905.05321">pdf</a>, <a href="https://arxiv.org/format/1905.05321">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.3390/universe5050125">10.3390/universe5050125 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Fifty years of energy extraction from rotating black hole: revisiting magnetic Penrose process </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Tursunov%2C+A">Arman Tursunov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1905.05321v2-abstract-short" style="display: inline;"> Magnetic Penrose process (MPP) is not only the most exciting and fascinating process mining the rotational energy of black hole but it is also the favored astrophysically viable mechanism for high energy sources and phenomena. It operates in three regimes of efficiency, namely low, moderate and ultra, depending on the magnetization and charging of spinning black holes in astrophysical setting. In… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.05321v2-abstract-full').style.display = 'inline'; document.getElementById('1905.05321v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1905.05321v2-abstract-full" style="display: none;"> Magnetic Penrose process (MPP) is not only the most exciting and fascinating process mining the rotational energy of black hole but it is also the favored astrophysically viable mechanism for high energy sources and phenomena. It operates in three regimes of efficiency, namely low, moderate and ultra, depending on the magnetization and charging of spinning black holes in astrophysical setting. In this paper, we revisit MPP with a comprehensive discussion of its physics in different regimes, and compare its operation with other competing mechanisms. We show that MPP could in principle foot the bill for powering engine of such phenomena as ultra-high-energy cosmic rays, relativistic jets, fast radio bursts, quasars, AGNs, etc. Further, it also leads to a number of important observable predictions. All this beautifully bears out the promise of a new vista of energy powerhouse heralded by Roger Penrose half a century ago through this process, and it has today risen in its magnetically empowered version of mid 1980s from a purely thought experiment of academic interest to a realistic powering mechanism for various high-energy astrophysical phenomena. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.05321v2-abstract-full').style.display = 'none'; document.getElementById('1905.05321v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 26 May, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 13 May, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">25 pages, 3 figures, 2 tables; published version, some references added; Invited Review for the special issue on Accretion Disks, Jets, GRBs and related Gravitational Waves; This work is dedicated to the fond memory of Dr. Sanjay Wagh, who was one of the initiators of work on magnetic Penrose process in his doctoral thesis in mid 1980s. He passed away on the day this paper appeared on arXiv</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Universe 5, 125, (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1905.01088">arXiv:1905.01088</a> <span> [<a href="https://arxiv.org/pdf/1905.01088">pdf</a>, <a href="https://arxiv.org/ps/1905.01088">ps</a>, <a href="https://arxiv.org/format/1905.01088">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.100.044001">10.1103/PhysRevD.100.044001 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Harmonic oscillations of neutral particles in the $纬$-metric </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Toshmatov%2C+B">Bobir Toshmatov</a>, <a href="/search/gr-qc?searchtype=author&query=Malafarina%2C+D">Daniele Malafarina</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1905.01088v2-abstract-short" style="display: inline;"> We consider a well-known static, axially symmetric, vacuum solution of Einstein equations belonging to Weyl's class and determine the fundamental frequencies of small harmonic oscillations of test particles around stable circular orbits in the equatorial plane. We discuss the radial profiles of frequencies of the radial, latitudinal (vertical), and azimuthal (Keplerian) harmonic oscillations relat… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.01088v2-abstract-full').style.display = 'inline'; document.getElementById('1905.01088v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1905.01088v2-abstract-full" style="display: none;"> We consider a well-known static, axially symmetric, vacuum solution of Einstein equations belonging to Weyl's class and determine the fundamental frequencies of small harmonic oscillations of test particles around stable circular orbits in the equatorial plane. We discuss the radial profiles of frequencies of the radial, latitudinal (vertical), and azimuthal (Keplerian) harmonic oscillations relative to the comoving and distant observers and compare with the corresponding ones in the Schwarzschild and Kerr geometries. We show that there exist latitudinal and radial frequencies of harmonic oscillations of particles moving along the circular orbits for which it is impossible to determine whether the central gravitating object is described by the slowly rotating Kerr solution or by a slightly deformed static space-time. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1905.01088v2-abstract-full').style.display = 'none'; document.getElementById('1905.01088v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 2 August, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 3 May, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages, 5 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 100, 044001 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1903.03436">arXiv:1903.03436</a> <span> [<a href="https://arxiv.org/pdf/1903.03436">pdf</a>, <a href="https://arxiv.org/ps/1903.03436">ps</a>, <a href="https://arxiv.org/format/1903.03436">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1088/1475-7516/2020/04/035">10.1088/1475-7516/2020/04/035 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Buchdahl compactness limit and gravitational field energy </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1903.03436v7-abstract-short" style="display: inline;"> The main aim of this paper is essentially to point out that the Buchdahl compactness limit of a static object is given by \it{gravitational field energy being less than or equal to half of its non-gravitational matter energy}. It is thus entirely determined without any reference to interior distribution by the exterior unique solutions, the Schwarzschild for neutral and the Reissner-Nordstr{… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1903.03436v7-abstract-full').style.display = 'inline'; document.getElementById('1903.03436v7-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1903.03436v7-abstract-full" style="display: none;"> The main aim of this paper is essentially to point out that the Buchdahl compactness limit of a static object is given by \it{gravitational field energy being less than or equal to half of its non-gravitational matter energy}. It is thus entirely determined without any reference to interior distribution by the exterior unique solutions, the Schwarzschild for neutral and the Reissner-Nordstr{$\ddot o$}m for charged object. In terms of surface potential, it reads as $桅(R) = (M-Q^2/2R)/R \leq 4/9$ which translates to surface red-shift being less than or equal to $3$. It also prescribes an upper bound on charge an object could have, $Q^2/M^2 \leq 9/8 > 1$. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1903.03436v7-abstract-full').style.display = 'none'; document.getElementById('1903.03436v7-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 April, 2020; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 4 March, 2019; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2019. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Almost matches with the published version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> JCAP 04(2020)035 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1810.08066">arXiv:1810.08066</a> <span> [<a href="https://arxiv.org/pdf/1810.08066">pdf</a>, <a href="https://arxiv.org/format/1810.08066">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> </div> <p class="title is-5 mathjax"> Electromagnetic field around boosted rotating black hole </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Abdujabbarov%2C+A">Ahmadjon Abdujabbarov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1810.08066v1-abstract-short" style="display: inline;"> The exact analytic solutions of the Maxwell equations in the exterior of a boosted rotating black hole immersed in an external magnetic field are obtained. The effect of boost as well as electromagnetic field on charged particle motion and energy extraction process -- magnetic Penrose process around black hole is studied. It justifies however the well known statement that magnetic field greatly in… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1810.08066v1-abstract-full').style.display = 'inline'; document.getElementById('1810.08066v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1810.08066v1-abstract-full" style="display: none;"> The exact analytic solutions of the Maxwell equations in the exterior of a boosted rotating black hole immersed in an external magnetic field are obtained. The effect of boost as well as electromagnetic field on charged particle motion and energy extraction process -- magnetic Penrose process around black hole is studied. It justifies however the well known statement that magnetic field greatly increases efficiency of energy extraction which is further boosted by the boost velocity. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1810.08066v1-abstract-full').style.display = 'none'; document.getElementById('1810.08066v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 17 October, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, 9 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1809.10457">arXiv:1809.10457</a> <span> [<a href="https://arxiv.org/pdf/1809.10457">pdf</a>, <a href="https://arxiv.org/ps/1809.10457">ps</a>, <a href="https://arxiv.org/format/1809.10457">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-019-7088-6">10.1140/epjc/s10052-019-7088-6 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The higher dimensional Myers-Perry black hole with single rotation always obeys the Cosmic Censorship Conjecture </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Shaymatov%2C+S">Sanjar Shaymatov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1809.10457v3-abstract-short" style="display: inline;"> Even though the Myers-Perry five dimensional rotating black hole with two rotations could be overspun by test particle accretion, yet it turns out as we show in this letter that it cannot do so for a single rotation. On the other hand it is known that there exists no extremal limit for a black hole with single rotation in dimensions greater than equal to six. It has been proven that all higher dim… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1809.10457v3-abstract-full').style.display = 'inline'; document.getElementById('1809.10457v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1809.10457v3-abstract-full" style="display: none;"> Even though the Myers-Perry five dimensional rotating black hole with two rotations could be overspun by test particle accretion, yet it turns out as we show in this letter that it cannot do so for a single rotation. On the other hand it is known that there exists no extremal limit for a black hole with single rotation in dimensions greater than equal to six. It has been proven that all higher dimensional ($>4$) rotating black holes with only one single rotation can never be overspun under test particle linear accretion and hence would always obey CCC in the weak form. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1809.10457v3-abstract-full').style.display = 'none'; document.getElementById('1809.10457v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 July, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 27 September, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">5 pages, no figures; Coincides with published version</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C 79 (2019) 585 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1807.02216">arXiv:1807.02216</a> <span> [<a href="https://arxiv.org/pdf/1807.02216">pdf</a>, <a href="https://arxiv.org/format/1807.02216">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-019-6662-2">10.1140/epjc/s10052-019-6662-2 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> On some novel features of the Kerr-Newman-NUT Spacetime </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Mukherjee%2C+S">Sajal Mukherjee</a>, <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1807.02216v2-abstract-short" style="display: inline;"> In this work we have presented a special class of Kerr-Newman-NUT black hole, having its horizon located precisely at $r=2M$, for $Q^{2}=l^{2}-a^{2}$, where $M$, $l$, $a$ and $Q$ are respectively mass, NUT, rotation and electric charge parameters of the black hole. Clearly this choice radically alters the causal structure as there exists no Cauchy horizon indicating spacelike nature of the singula… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1807.02216v2-abstract-full').style.display = 'inline'; document.getElementById('1807.02216v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1807.02216v2-abstract-full" style="display: none;"> In this work we have presented a special class of Kerr-Newman-NUT black hole, having its horizon located precisely at $r=2M$, for $Q^{2}=l^{2}-a^{2}$, where $M$, $l$, $a$ and $Q$ are respectively mass, NUT, rotation and electric charge parameters of the black hole. Clearly this choice radically alters the causal structure as there exists no Cauchy horizon indicating spacelike nature of the singularity when it exists. On the other hand, there is no curvature singularity for $l^2 > a^2$, however it may have conical singularities. Furthermore there is no upper bound on specific rotation parameter $a/M$, which could exceed unity without risking destruction of the horizon. To bring out various discerning features of this special member of the Kerr-Newman-NUT family, we study timelike and null geodesics in the equatorial as well as off the equatorial plane, energy extraction through super-radiance and Penrose process, thermodynamical properties and also the quasi-periodic oscillations. It turns out that the black hole under study radiates less energy through the super-radiant modes and Penrose process than the other black holes in this family. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1807.02216v2-abstract-full').style.display = 'none'; document.getElementById('1807.02216v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 2 March, 2019; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 5 July, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Revised version, 37 pages, 10 figures, 1 table</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C 79, 161 (2019) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1804.09679">arXiv:1804.09679</a> <span> [<a href="https://arxiv.org/pdf/1804.09679">pdf</a>, <a href="https://arxiv.org/ps/1804.09679">ps</a>, <a href="https://arxiv.org/format/1804.09679">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1093/mnrasl/sly073">10.1093/mnrasl/sly073 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> The distinguishing signature of Magnetic Penrose Process </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Tursunov%2C+A">Arman Tursunov</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a>, <a href="/search/gr-qc?searchtype=author&query=Stuchl%C3%ADk%2C+Z">Zden臎k Stuchl铆k</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1804.09679v1-abstract-short" style="display: inline;"> In this Letter, we wish to point out that the distinguishing feature of Magnetic Penrose process (MPP) is its super high efficiency exceeding $100\%$ (which was established in mid 1980s for discrete particle accretion) of extraction of rotational energy of a rotating black hole electromagnetically for a magnetic field of milli Gauss order. Another similar process, which is also driven by electroma… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1804.09679v1-abstract-full').style.display = 'inline'; document.getElementById('1804.09679v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1804.09679v1-abstract-full" style="display: none;"> In this Letter, we wish to point out that the distinguishing feature of Magnetic Penrose process (MPP) is its super high efficiency exceeding $100\%$ (which was established in mid 1980s for discrete particle accretion) of extraction of rotational energy of a rotating black hole electromagnetically for a magnetic field of milli Gauss order. Another similar process, which is also driven by electromagnetic field, is Blandford-Znajek mechanism (BZ), which could be envisaged as high magnetic field limit MPP as it requires threshold magnetic field of order $10^4$G. Recent simulation studies of fully relativistic magnetohydrodynamic flows have borne out super high efficiency signature of the process for high magnetic field regime; viz BZ. We would like to make a clear prediction that similar simulation studies of MHD flows for low magnetic field regime, where BZ would be inoperative, would also have super efficiency. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1804.09679v1-abstract-full').style.display = 'none'; document.getElementById('1804.09679v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 25 April, 2018; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2018. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages, 1 figure, accepted to MNRAS Letters</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1703.05663">arXiv:1703.05663</a> <span> [<a href="https://arxiv.org/pdf/1703.05663">pdf</a>, <a href="https://arxiv.org/ps/1703.05663">ps</a>, <a href="https://arxiv.org/format/1703.05663">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.96.084058">10.1103/PhysRevD.96.084058 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Generalized G枚del universes in higher dimensions and pure Lovelock gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Molina%2C+A">Alfred Molina</a>, <a href="/search/gr-qc?searchtype=author&query=Pons%2C+J+M">Josep M. Pons</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1703.05663v1-abstract-short" style="display: inline;"> G枚del universe is a homogeneous rotating dust with negative $螞$ which is a direct product of three dimensional pure rotation metric with a line. We would generalize it to higher dimensions for Einstein and pure Lovelock gravity with only one $N$th order term. For higher dimensional generalization, we have to include more rotations in the metric, and hence we shall begin with the corresponding pure… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1703.05663v1-abstract-full').style.display = 'inline'; document.getElementById('1703.05663v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1703.05663v1-abstract-full" style="display: none;"> G枚del universe is a homogeneous rotating dust with negative $螞$ which is a direct product of three dimensional pure rotation metric with a line. We would generalize it to higher dimensions for Einstein and pure Lovelock gravity with only one $N$th order term. For higher dimensional generalization, we have to include more rotations in the metric, and hence we shall begin with the corresponding pure rotation odd $(d=2n+1)$-dimensional metric involving $n$ rotations, which eventually can be extended by a direct product with a line or a space of constant curvature for yielding higher dimensional G枚del universe. The considerations of $n$ rotations and also of constant curvature spaces is a new line of generalization and is being considered for the first time. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1703.05663v1-abstract-full').style.display = 'none'; document.getElementById('1703.05663v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 16 March, 2017; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2017. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">31 pages</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 96, 084058 (2017) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1609.02138">arXiv:1609.02138</a> <span> [<a href="https://arxiv.org/pdf/1609.02138">pdf</a>, <a href="https://arxiv.org/ps/1609.02138">ps</a>, <a href="https://arxiv.org/format/1609.02138">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/978-3-319-51700-1_7">10.1007/978-3-319-51700-1_7 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Understanding General Relativity after 100 years: A matter of perspective </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1609.02138v1-abstract-short" style="display: inline;"> This is the centenary year of general relativity, it is therefore natural to reflect on what perspective we have evolved in 100 years. I wish to share here a novel perspective, and the insights and directions that ensue from it. </span> <span class="abstract-full has-text-grey-dark mathjax" id="1609.02138v1-abstract-full" style="display: none;"> This is the centenary year of general relativity, it is therefore natural to reflect on what perspective we have evolved in 100 years. I wish to share here a novel perspective, and the insights and directions that ensue from it. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1609.02138v1-abstract-full').style.display = 'none'; document.getElementById('1609.02138v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 7 September, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">v1, 16pp; contribution to Paddy's Festschrift</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> in Gravity and the Quantum, eds J S Bagla, S Enginner, (Springer, 2017), pp. 73-87 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1607.07095">arXiv:1607.07095</a> <span> [<a href="https://arxiv.org/pdf/1607.07095">pdf</a>, <a href="https://arxiv.org/format/1607.07095">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Cosmology and Nongalactic Astrophysics">astro-ph.CO</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1142/S0218271817500560">10.1142/S0218271817500560 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Compact objects in pure Lovelock theory </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Hansraj%2C+S">Sudan Hansraj</a>, <a href="/search/gr-qc?searchtype=author&query=Chilambwe%2C+B">Brian Chilambwe</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1607.07095v2-abstract-short" style="display: inline;"> For static fluid interiors of compact objects in pure Lovelock gravity (involving ony one $N$th order term in the equation) we establish similarity in solutions for the critical odd and even $d=2N+1, 2N+2$ dimensions. It turns out that in critical odd $d=2N+1$ dimensions, there can exist no bound distribution with a finite radius, while in critical even $d=2N+2$ dimensions, all solutions have simi… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1607.07095v2-abstract-full').style.display = 'inline'; document.getElementById('1607.07095v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1607.07095v2-abstract-full" style="display: none;"> For static fluid interiors of compact objects in pure Lovelock gravity (involving ony one $N$th order term in the equation) we establish similarity in solutions for the critical odd and even $d=2N+1, 2N+2$ dimensions. It turns out that in critical odd $d=2N+1$ dimensions, there can exist no bound distribution with a finite radius, while in critical even $d=2N+2$ dimensions, all solutions have similar behavior. For exhibition of similarity we would compare star solutions for $N =1, 2$ in $d=4$ Einstein and $d=6$ in Gauss-Bonnet theory respectively. We also obtain the pure Lovelock analogue of the Finch-Skea model. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1607.07095v2-abstract-full').style.display = 'none'; document.getElementById('1607.07095v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 May, 2017; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 24 July, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">22 pages 3 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1607.06229">arXiv:1607.06229</a> <span> [<a href="https://arxiv.org/pdf/1607.06229">pdf</a>, <a href="https://arxiv.org/format/1607.06229">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/s10714-017-2259-y">10.1007/s10714-017-2259-y <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Buchdahl-Vaidya-Tikekar model for stellar interior in pure Lovelock gravity - II </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Molina%2C+A">Alfred Molina</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Khugaev%2C+A">Avas Khugaev</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1607.06229v1-abstract-short" style="display: inline;"> For a given Lovelock order $N$, it turns out that static fluid solutions of the pure Lovelock equation for a star interior have the universal behavior in all $n\geq 2N+2$ dimensions relative to an appropriately defined variable and the Vaidya-Tikekar parameter $K$, indicating deviation from sphericity of $3$-space geometry. We employ the Buchdahl metric ansatz which encompasses almost all the know… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1607.06229v1-abstract-full').style.display = 'inline'; document.getElementById('1607.06229v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1607.06229v1-abstract-full" style="display: none;"> For a given Lovelock order $N$, it turns out that static fluid solutions of the pure Lovelock equation for a star interior have the universal behavior in all $n\geq 2N+2$ dimensions relative to an appropriately defined variable and the Vaidya-Tikekar parameter $K$, indicating deviation from sphericity of $3$-space geometry. We employ the Buchdahl metric ansatz which encompasses almost all the known physically acceptable models including in particular the Vaidya-Tikekar and Finch-Skea. Further for a given star radius, the constant density star, always described by the Schwarzschild interior solution, defines the most compact state of distribution while the other end is marked by the Finch-Skea model, and all the other physically tenable models lie in between these two limiting distributions. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1607.06229v1-abstract-full').style.display = 'none'; document.getElementById('1607.06229v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 21 July, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> July 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">18 pages, 7 figures</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1606.01330">arXiv:1606.01330</a> <span> [<a href="https://arxiv.org/pdf/1606.01330">pdf</a>, <a href="https://arxiv.org/ps/1606.01330">ps</a>, <a href="https://arxiv.org/format/1606.01330">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.95.064059">10.1103/PhysRevD.95.064059 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Buchdahl compactness limit for a pure Lovelock static fluid star </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1606.01330v4-abstract-short" style="display: inline;"> We obtain the Buchdahl compactness limit for a pure Lovelock static fluid star and verify that the limit following from the uniform density Schwarzschild's interior solution, which is universal irrespective of the gravitational theory (Einstein or Lovelock), is true in general. In terms of surface potential $桅(r)$, it means at the surface of the star $r=r_{0}$, $桅(r_{0}) < 2N(d-N-1)/(d-1)^2$ where… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1606.01330v4-abstract-full').style.display = 'inline'; document.getElementById('1606.01330v4-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1606.01330v4-abstract-full" style="display: none;"> We obtain the Buchdahl compactness limit for a pure Lovelock static fluid star and verify that the limit following from the uniform density Schwarzschild's interior solution, which is universal irrespective of the gravitational theory (Einstein or Lovelock), is true in general. In terms of surface potential $桅(r)$, it means at the surface of the star $r=r_{0}$, $桅(r_{0}) < 2N(d-N-1)/(d-1)^2$ where $d$, $N$ respectively indicate spacetime dimensions and Lovelock order. For a given $N$, $桅(r_{0})$ is maximum for $d=2N+2$ while it is always $4/9$, Buchdahl's limit, for $d=3N+1$. It is also remarkable that for $N=1$ Einstein gravity, or for pure Lovelock in $d=3N+1$, Buchdahl's limit is equivalent to the criteria that gravitational field energy exterior to the star is less than half its gravitational mass, having no reference to the interior at all. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1606.01330v4-abstract-full').style.display = 'none'; document.getElementById('1606.01330v4-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 5 June, 2017; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 4 June, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> June 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">Revised; Title Changed; 11 pages; no figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 95, 064059 (2017) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1605.01961">arXiv:1605.01961</a> <span> [<a href="https://arxiv.org/pdf/1605.01961">pdf</a>, <a href="https://arxiv.org/ps/1605.01961">ps</a>, <a href="https://arxiv.org/format/1605.01961">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Cosmology and Nongalactic Astrophysics">astro-ph.CO</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-018-5546-1">10.1140/epjc/s10052-018-5546-1 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> 1/r potential in higher dimensions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1605.01961v2-abstract-short" style="display: inline;"> In Einstein gravity, gravitational potential goes as $1/r^{d-3}$ in $d$ non-compactified spacetime dimensions, which assumes the familiar $1/r$ form in four dimensions. On the other hand, it goes as $1/r^伪$, with $伪=(d-2m-1)/m$, in pure Lovelock gravity involving only one $m$th order term of the Lovelock polynomial in the gravitational action. The latter offers a novel possibility of having $1/r$… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1605.01961v2-abstract-full').style.display = 'inline'; document.getElementById('1605.01961v2-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1605.01961v2-abstract-full" style="display: none;"> In Einstein gravity, gravitational potential goes as $1/r^{d-3}$ in $d$ non-compactified spacetime dimensions, which assumes the familiar $1/r$ form in four dimensions. On the other hand, it goes as $1/r^伪$, with $伪=(d-2m-1)/m$, in pure Lovelock gravity involving only one $m$th order term of the Lovelock polynomial in the gravitational action. The latter offers a novel possibility of having $1/r$ potential for the non-compactified dimension spectrum given by $d=3m+1$. Thus it turns out that in the two prototype gravitational settings of isolated objects, like black holes and the universe as a whole --- cosmological models, the Einstein gravity in four and $m$th order pure Lovelock gravity in $3m+1$ dimensions behave in a similar fashion as far as gravitational interactions are considered. However propagation of gravitational waves (or the number of degrees of freedom) does indeed serve as a discriminator because it has two polarizations only in four dimensions. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1605.01961v2-abstract-full').style.display = 'none'; document.getElementById('1605.01961v2-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 31 January, 2018; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 4 May, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> May 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">8 pages, no figures; Revised version, title changed;</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Eur. Phys. J. C 78, 81 (2018) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1604.01054">arXiv:1604.01054</a> <span> [<a href="https://arxiv.org/pdf/1604.01054">pdf</a>, <a href="https://arxiv.org/ps/1604.01054">ps</a>, <a href="https://arxiv.org/format/1604.01054">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> (Not so) pure Lovelock Kasner metrics </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Camanho%2C+X+O">Xi谩n O. Camanho</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Molina%2C+A">Alfred Molina</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1604.01054v1-abstract-short" style="display: inline;"> The gravitational interaction is expected to be modified for very short distances. This is particularly important in situations in which the curvature of spacetime is large in general, such as close to the initial cosmological singularity. The gravitational dynamics is then captured by the higher curvature terms in the action, making it difficult to reliably extrapolate any prediction of general r… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1604.01054v1-abstract-full').style.display = 'inline'; document.getElementById('1604.01054v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1604.01054v1-abstract-full" style="display: none;"> The gravitational interaction is expected to be modified for very short distances. This is particularly important in situations in which the curvature of spacetime is large in general, such as close to the initial cosmological singularity. The gravitational dynamics is then captured by the higher curvature terms in the action, making it difficult to reliably extrapolate any prediction of general relativity. In this note we review pure Lovelock equations for Kasner-type metrics. These equations correspond to a single $N$th order Lovelock term in the action in $d=2N+1,\,2N+2$ dimensions, and they capture the relevant gravitational dynamics when aproaching the big-bang singularity within the Lovelock family of theories. These are classified in several isotropy types. Some of these families correspond to degenerate classes of solutions, such that their dynamics is not completely determined by the equations of pure Lovelock gravity. Instead, these Kasner solutions become sensitive to the subleading terms in the Lovelock series. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1604.01054v1-abstract-full').style.display = 'none'; document.getElementById('1604.01054v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 4 April, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> April 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">9 pages, no figures. Prepared for the Proceedings of the Fourteenth Marcel Grossman Meeting on General Relativity, edited by Massimo Bianchi, Robert T. Jantzen and Remo Ruffini. World Scientific, Singapore, 2016</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1603.07118">arXiv:1603.07118</a> <span> [<a href="https://arxiv.org/pdf/1603.07118">pdf</a>, <a href="https://arxiv.org/format/1603.07118">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.94.064065">10.1103/PhysRevD.94.064065 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Higher dimensional generalization of Buchdahl-Vaidya-Tikekar model for super compact star </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Khugaev%2C+A">Avas Khugaev</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Molina%2C+A">Alfred Molina</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1603.07118v1-abstract-short" style="display: inline;"> We obtain higher dimensional solutions for super compact star for the Buchdahl-Vaidya-Tikekar metric ansatz. In particular, Vaidya and Tikekar characterized the $3$-geometry by a parameter, $K$ which is related to the sign of density gradient. It turns out that the key pressure isotropy equation continues to have the same Gauss form, and hence $4$-dimensional solutions can be taken over to higher… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1603.07118v1-abstract-full').style.display = 'inline'; document.getElementById('1603.07118v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1603.07118v1-abstract-full" style="display: none;"> We obtain higher dimensional solutions for super compact star for the Buchdahl-Vaidya-Tikekar metric ansatz. In particular, Vaidya and Tikekar characterized the $3$-geometry by a parameter, $K$ which is related to the sign of density gradient. It turns out that the key pressure isotropy equation continues to have the same Gauss form, and hence $4$-dimensional solutions can be taken over to higher dimensions with $K$ satisfying the relation, $K_n = (K_4-n+4)/(n-3)$ where subscript refers to dimension of spacetime. Further $K\geq0$ is required else density would have undesirable feature of increasing with radius, and the equality indicates a constant density star described by the Schwarzschild interior solution. This means for a given $K_4$, maximum dimension could only be $n=K_4+4$, else $K_n$ will turn negative. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1603.07118v1-abstract-full').style.display = 'none'; document.getElementById('1603.07118v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 23 March, 2016; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> March 2016. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">13 pages, 6 figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 94, 064065 (2016) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1511.02541">arXiv:1511.02541</a> <span> [<a href="https://arxiv.org/pdf/1511.02541">pdf</a>, <a href="https://arxiv.org/ps/1511.02541">ps</a>, <a href="https://arxiv.org/format/1511.02541">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.93.064009">10.1103/PhysRevD.93.064009 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Dynamical structure of Pure Lovelock gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Durka%2C+R">Remigiusz Durka</a>, <a href="/search/gr-qc?searchtype=author&query=Merino%2C+N">Nelson Merino</a>, <a href="/search/gr-qc?searchtype=author&query=Miskovic%2C+O">Olivera Miskovic</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1511.02541v1-abstract-short" style="display: inline;"> We study dynamical structure of Pure Lovelock gravity in spacetime dimensions higher than four using the Hamiltonian formalism. The action consists of cosmological constant and a single higher-order polynomial in the Riemann tensor. Similarly to Einstein-Hilbert action, it possesses a unique constant curvature vacuum and charged black hole solutions. We analyze physical degrees of freedom and loca… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1511.02541v1-abstract-full').style.display = 'inline'; document.getElementById('1511.02541v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1511.02541v1-abstract-full" style="display: none;"> We study dynamical structure of Pure Lovelock gravity in spacetime dimensions higher than four using the Hamiltonian formalism. The action consists of cosmological constant and a single higher-order polynomial in the Riemann tensor. Similarly to Einstein-Hilbert action, it possesses a unique constant curvature vacuum and charged black hole solutions. We analyze physical degrees of freedom and local symmetries in this theory. In contrast to the Einstein-Hilbert case, a number of degrees of freedom depends on the background and can vary from zero to the maximal value carried by the Lovelock theory. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1511.02541v1-abstract-full').style.display = 'none'; document.getElementById('1511.02541v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 8 November, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">23 pages, no figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 93, 064009 (2016) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1511.02241">arXiv:1511.02241</a> <span> [<a href="https://arxiv.org/pdf/1511.02241">pdf</a>, <a href="https://arxiv.org/ps/1511.02241">ps</a>, <a href="https://arxiv.org/format/1511.02241">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="History and Philosophy of Physics">physics.hist-ph</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> General Relativity in Post Independence India </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1511.02241v3-abstract-short" style="display: inline;"> The most outstanding contribution to general relativity in this era came in 1953 (published in 1955 \cite{akr}) in the form of the Raychaudhri equation. It is in 1960s that the observations began to confront the eupherial theory and thus began exploration of GR as a legitimate physical theory in right earnest. The remarkable discoveries of cosmic microwave background radiation, quasars, rotating K… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1511.02241v3-abstract-full').style.display = 'inline'; document.getElementById('1511.02241v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1511.02241v3-abstract-full" style="display: none;"> The most outstanding contribution to general relativity in this era came in 1953 (published in 1955 \cite{akr}) in the form of the Raychaudhri equation. It is in 1960s that the observations began to confront the eupherial theory and thus began exploration of GR as a legitimate physical theory in right earnest. The remarkable discoveries of cosmic microwave background radiation, quasars, rotating Kerr black hole and the powerful singularity theorems heralded a new canvas of relativistic astrophysics and cosmology. I would attempt to give a brief account of Indian participation in these exciting times. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1511.02241v3-abstract-full').style.display = 'none'; document.getElementById('1511.02241v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 22 December, 2015; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 3 November, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> November 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">27 pages, latex, Published in Current Science: Special Issue on 100 Years of General Relativity edited by Banibrata Mukhopadhya and T P Singh</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Current Science Vol. 109 (N0. 12, 25 December 2015), 2220-2229 (2015) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1510.07490">arXiv:1510.07490</a> <span> [<a href="https://arxiv.org/pdf/1510.07490">pdf</a>, <a href="https://arxiv.org/ps/1510.07490">ps</a>, <a href="https://arxiv.org/format/1510.07490">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1103/PhysRevD.93.044072">10.1103/PhysRevD.93.044072 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Universality of isothermal fluid spheres in Lovelock gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Hansraj%2C+S">Sudan Hansraj</a>, <a href="/search/gr-qc?searchtype=author&query=Maharaj%2C+S+D">Sunil D. Maharaj</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1510.07490v1-abstract-short" style="display: inline;"> We show universality of isothermal fluid spheres in pure Lovelock gravity where the equation of motion has only one $N$th order term coming from the corresponding Lovelock polynomial action of degree $N$. Isothermality is characterized by the equation of state, $p = 伪蟻$ and the property, $蟻\sim 1/r^{2N}$. Then the solution describing isothermal spheres, which exist only for the pure Lovelock equat… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1510.07490v1-abstract-full').style.display = 'inline'; document.getElementById('1510.07490v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1510.07490v1-abstract-full" style="display: none;"> We show universality of isothermal fluid spheres in pure Lovelock gravity where the equation of motion has only one $N$th order term coming from the corresponding Lovelock polynomial action of degree $N$. Isothermality is characterized by the equation of state, $p = 伪蟻$ and the property, $蟻\sim 1/r^{2N}$. Then the solution describing isothermal spheres, which exist only for the pure Lovelock equation, is of the same form for the general Lovelock degree $N$ in all dimenions $d \geq 2N+2$. We further prove that the necessary and sufficient condition for the isothermal sphere is that its metric is conformal to the massless global monopole or the solid angle deficit metric, and this feature is also universal. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1510.07490v1-abstract-full').style.display = 'none'; document.getElementById('1510.07490v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 26 October, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> October 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">11 pages</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> Phys. Rev. D 93, 044072 (2016) </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1509.02156">arXiv:1509.02156</a> <span> [<a href="https://arxiv.org/pdf/1509.02156">pdf</a>, <a href="https://arxiv.org/ps/1509.02156">ps</a>, <a href="https://arxiv.org/format/1509.02156">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1007/JHEP12(2015)003">10.1007/JHEP12(2015)003 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Brown-York quasilocal energy in Lanczos-Lovelock gravity and black hole horizons </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Chakraborty%2C+S">Sumanta Chakraborty</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1509.02156v3-abstract-short" style="display: inline;"> A standard candidate for quasilocal energy in general relativity is the Brown-York energy, which is essentially a two dimensional surface integral of the extrinsic curvature on the two-boundary of a spacelike hypersurface referenced to flat spacetime. Several years back one of us had conjectured that the black hole horizon is defined by equipartition of gravitational and non-gravitational energy.… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1509.02156v3-abstract-full').style.display = 'inline'; document.getElementById('1509.02156v3-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1509.02156v3-abstract-full" style="display: none;"> A standard candidate for quasilocal energy in general relativity is the Brown-York energy, which is essentially a two dimensional surface integral of the extrinsic curvature on the two-boundary of a spacelike hypersurface referenced to flat spacetime. Several years back one of us had conjectured that the black hole horizon is defined by equipartition of gravitational and non-gravitational energy. By employing the above definition of quasilocal Brown-York energy, we have verified the equipartition conjecture for static charged and charged axi-symmetric blck holes in general relativity. We have further generalized the Brown-York formalism to all orders in Lanczos-Lovelock theories of gravity and have verified the conjecture for pure Lovelock charged black hole in all even d=2m+2 dimensions, where m is the degree of Lovelock action. It turns out that the equipartition conjecture works only for pure Lovelock, and not for Einstein-Lovelock, black holes. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1509.02156v3-abstract-full').style.display = 'none'; document.getElementById('1509.02156v3-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 December, 2015; <span class="has-text-black-bis has-text-weight-semibold">v1</span> submitted 7 September, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">v2, References added, 18 pages, No figures</span> </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Journal ref:</span> JHEP 12(2015)003 </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1509.00706">arXiv:1509.00706</a> <span> [<a href="https://arxiv.org/pdf/1509.00706">pdf</a>, <a href="https://arxiv.org/ps/1509.00706">ps</a>, <a href="https://arxiv.org/format/1509.00706">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="Cosmology and Nongalactic Astrophysics">astro-ph.CO</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Physics - Theory">hep-th</span> </div> </div> <p class="title is-5 mathjax"> The cosmological constant from the zero point energy of compact dimensions </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Soni%2C+V">Vikram Soni</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Adhikari%2C+R">Rathin Adhikari</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1509.00706v1-abstract-short" style="display: inline;"> We consider extra compact dimensions as the origin of a cosmological universal energy density in the regular dimensions, with only graviton fields propagating in the compact space dimensions. The quantum zero point energy originating from the finite size boundary condition in the compact dimensions can produce a constant energy density in regular $3$ space which is homogeneous and isotropic. It th… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1509.00706v1-abstract-full').style.display = 'inline'; document.getElementById('1509.00706v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1509.00706v1-abstract-full" style="display: none;"> We consider extra compact dimensions as the origin of a cosmological universal energy density in the regular dimensions, with only graviton fields propagating in the compact space dimensions. The quantum zero point energy originating from the finite size boundary condition in the compact dimensions can produce a constant energy density in regular $3$ space which is homogeneous and isotropic. It then makes a natural identification with the cosmological constant in conformity with the Einstein equation. It turns out that for the emergent energy density to agree with the observed value of the cosmological constant, the size/radius of compact dimension is to be of order of $10^{-2}$ cm. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1509.00706v1-abstract-full').style.display = 'none'; document.getElementById('1509.00706v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 2 September, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> September 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">6 pages</span> </p> </li> <li class="arxiv-result"> <div class="is-marginless"> <p class="list-title is-inline-block"><a href="https://arxiv.org/abs/1508.00331">arXiv:1508.00331</a> <span> [<a href="https://arxiv.org/pdf/1508.00331">pdf</a>, <a href="https://arxiv.org/ps/1508.00331">ps</a>, <a href="https://arxiv.org/format/1508.00331">other</a>] </span> </p> <div class="tags is-inline-block"> <span class="tag is-small is-link tooltip is-tooltip-top" data-tooltip="General Relativity and Quantum Cosmology">gr-qc</span> <span class="tag is-small is-grey tooltip is-tooltip-top" data-tooltip="High Energy Astrophysical Phenomena">astro-ph.HE</span> </div> <div class="is-inline-block" style="margin-left: 0.5rem"> <div class="tags has-addons"> <span class="tag is-dark is-size-7">doi</span> <span class="tag is-light is-size-7"><a class="" href="https://doi.org/10.1140/epjc/s10052-015-3604-5">10.1140/epjc/s10052-015-3604-5 <i class="fa fa-external-link" aria-hidden="true"></i></a></span> </div> </div> </div> <p class="title is-5 mathjax"> Energetics and optical properties of $6$-dimensional rotating black hole in pure Gauss-Bonnet gravity </p> <p class="authors"> <span class="search-hit">Authors:</span> <a href="/search/gr-qc?searchtype=author&query=Abdujabbarov%2C+A">Ahmadjon Abdujabbarov</a>, <a href="/search/gr-qc?searchtype=author&query=Atamurotov%2C+F">Farruh Atamurotov</a>, <a href="/search/gr-qc?searchtype=author&query=Dadhich%2C+N">Naresh Dadhich</a>, <a href="/search/gr-qc?searchtype=author&query=Ahmedov%2C+B">Bobomurat Ahmedov</a>, <a href="/search/gr-qc?searchtype=author&query=Stuchl%C3%ADk%2C+Z">Zden臎k Stuchl铆k</a> </p> <p class="abstract mathjax"> <span class="has-text-black-bis has-text-weight-semibold">Abstract</span>: <span class="abstract-short has-text-grey-dark mathjax" id="1508.00331v1-abstract-short" style="display: inline;"> We study physical processes around a rotating black hole in pure Gauss-Bonnet (GB) gravity. In pure GB gravity, gravitational potential has slower fall off as compared to the corresponding Einstein potential in the same dimension. It is therefore expected that the energetics of pure GB black hole would be weaker, and our analysis bears out that the efficiency of energy extraction by Penrose proces… <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1508.00331v1-abstract-full').style.display = 'inline'; document.getElementById('1508.00331v1-abstract-short').style.display = 'none';">▽ More</a> </span> <span class="abstract-full has-text-grey-dark mathjax" id="1508.00331v1-abstract-full" style="display: none;"> We study physical processes around a rotating black hole in pure Gauss-Bonnet (GB) gravity. In pure GB gravity, gravitational potential has slower fall off as compared to the corresponding Einstein potential in the same dimension. It is therefore expected that the energetics of pure GB black hole would be weaker, and our analysis bears out that the efficiency of energy extraction by Penrose process is increased to $25.8\%$ and particle acceleration is increased to $55.28\%$, and optical shadow of the black hole is decreased. These are the distinguishing in principle observable features of pure GB black hole. <a class="is-size-7" style="white-space: nowrap;" onclick="document.getElementById('1508.00331v1-abstract-full').style.display = 'none'; document.getElementById('1508.00331v1-abstract-short').style.display = 'inline';">△ Less</a> </span> </p> <p class="is-size-7"><span class="has-text-black-bis has-text-weight-semibold">Submitted</span> 3 August, 2015; <span class="has-text-black-bis has-text-weight-semibold">originally announced</span> August 2015. </p> <p class="comments is-size-7"> <span class="has-text-black-bis has-text-weight-semibold">Comments:</span> <span class="has-text-grey-dark mathjax">10 pages, 8 figures</span> </p> </li> </ol> <nav class="pagination is-small is-centered breathe-horizontal" role="navigation" aria-label="pagination"> <a href="" class="pagination-previous is-invisible">Previous </a> <a href="/search/?searchtype=author&query=Dadhich%2C+N&start=50" class="pagination-next" 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