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Ronggen Cai - One of the best experts on this subject based on the ideXlab platform.
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gauss bonnet Black Holes in ads spaces
Physical Review D, 2004Co-Authors: Ronggen CaiAbstract:We study the thermodynamic properties and phase structures of topological Black Holes in Einstein theory with a Gauss-Bonnet term and a negative cosmological constant. The event horizon of these topological Black Holes can be a hypersurface with positive, zero, or negative constant curvature. When the horizon is a zero curvature hypersurface, the thermodynamic properties of Black Holes are completely the same as those of Black Holes without the Gauss-Bonnet term, although the two Black hole solutions are quite different. When the horizon is a negative constant curvature hypersurface, the thermodynamic properties of the Gauss-Bonnet Black Holes are qualitatively similar to those of Black Holes without the Gauss-Bonnet term. When the event horizon is a hypersurface with positive constant curvature, we find that the thermodynamic properties and phase structures of Black Holes drastically depend on the spacetime dimension d and the coefficient of the Gauss-Bonnet term: when dgreater than or equal to6, the properties of Black Holes are also qualitatively similar to the case without the Gauss-Bonnet term, but when d=5, a new phase of locally stable small Blacks Holes occurs under a critical value of the Gauss-Bonnet coefficient, and beyond the critical value, the Black Holes are always thermodynamically stable. However, the locally stable small Black hole is not globally preferred; instead a thermal anti-de Sitter space is globally preferred. We find that there is a minimal horizon radius, below which the Hawking-Page phase transition will not occur since for these Black Holes the thermal anti-de Sitter space is always globally preferred.
Peihung Yuan - One of the best experts on this subject based on the ideXlab platform.
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rotating Black Holes and coriolis effect
Physics Letters B, 2016Co-Authors: Chiajui Chou, Xiaoning Wu, Yi Yang, Peihung YuanAbstract:Abstract In this work, we consider the fluid/gravity correspondence for general rotating Black Holes. By using the suitable boundary condition in near horizon limit, we study the correspondence between gravitational perturbation and fluid equation. We find that the dual fluid equation for rotating Black Holes contains a Coriolis force term, which is closely related to the angular velocity of the Black hole horizon. This can be seen as a dual effect for the frame-dragging effect of rotating Black hole under the holographic picture.
Ghosh, Sushant G. - One of the best experts on this subject based on the ideXlab platform.
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Strong field gravitational lensing by hairy Kerr Black Holes
2021Co-Authors: Shafqat Ul Islam, Ghosh, Sushant G.Abstract:The recent time witnessed a surge of interest in strong gravitational lensing by Black Holes due to the Event Horizon Telescope (EHT) results, suggesting comparing the Black hole lensing in general relativity and modified gravity theories. That may help us to assess the phenomenological differences between these models. A Kerr Black hole is also a solution to some alternative theories of gravity, while recently obtained modified Kerr Black Holes (hairy Kerr Black Holes), which evade the no-hair theorem, are due to additional sources the surrounding fluid, like dark matter, having conserved energy momentum tensor (EMT). These hairy Kerr Black Holes may be solutions to an alternative theory of gravity. We generalize previous work on gravitational lensing by a Kerr Black hole, in the strong deflection limits to the hairy Kerr Black Holes, with deviation parameter $\alpha$ and a primary hair $\ell_0$. Interestingly, the deflection coefficient $\bar{a}$, respectively, increases and decreases with increasing $\ell_0$ and $\alpha$. $\bar{b}$ shows opposite behaviour with $\ell_0$ and $\alpha$. We also find that the deflection angle $\alpha_D$, angular position $\theta_{\infty}$ and $u_{m}$ decreases, but angular separation $s$ increases with $\alpha$. We compare our results with those for Kerr Black Holes, and also, the formalism is applied to discuss the astrophysical consequences in the context of the supermassive Black Holes Sgr A* and M87*. We observe that the deviations of the angular positions from that of the Kerr Black hole are not more than $2.6~\mu$as for Sgr A* and $1.96~\mu$as for M87*, which are unlikely to get resolved by the current EHT observations.Comment: 17 pages, 8 figures, 8 tables. Some text change
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Strong field gravitational lensing by hairy Kerr Black Holes
2021Co-Authors: Shafqat Ul Islam, Ghosh, Sushant G.Abstract:Recent times witnessed a surge of interest in strong gravitational lensing by Black Holes due to the Event Horizon Telescope (EHT) results, which suggest comparing the Black hole lensing in general relativity and modified gravity theories. This may help us to assess the phenomenological differences between these models. A Kerr Black hole is also a solution to some alternative theories of gravity, while recently obtained modified Kerr Black Holes (hairy Kerr Black Holes), which evade the no-hair theorem, are due to additional sources from surrounding fluid, like dark matter, having conserved energy momentum tensor (EMT). These hairy Kerr Black Holes may also be solutions to an alternative theory of gravity. We generalize previous work on gravitational lensing by a Kerr Black hole in the strong deflection limits to the hairy Kerr Black Holes, with a deviation parameter $\alpha$ and a primary hair $\ell_0$. Interestingly, the deflection coefficient $\bar{a}$ increases and decreases with increasing $\ell_0$ and $\alpha$ respectively. $\bar{b}$ shows opposite behaviour with $\ell_0$ and $\alpha$. We also find that the deflection angle $\alpha_D$, angular position $\theta_{\infty}$ and $u_{m}$ decrease, but angular separation $s$ increases with $\alpha$. We compare our results with those for Kerr Black Holes, and also apply the formalism to discuss the astrophysical consequences in the context of the supermassive Black Holes Sgr A* and M87*. We observe that the deviations of the angular positions from that of the Kerr Black hole are not more than $2.6~\mu$as for Sgr A* and $1.96~\mu$as for M87*, which are unlikely to be resolved by the current EHT observations.Comment: 17 pages, 7 figures, 8 tables, minor typos corrected, accepted in Phys. Rev.
Gregory Ruth - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamics of Many Black Holes
'Frontiers Media SA', 2021Co-Authors: Gregory Ruth, Lim, Zheng Liang, Scoins AndrewAbstract:We discuss the thermodynamics of an array of collinear Black Holes which may be accelerating. We prove a general First Law, including variations in the tensions of strings linking and accelerating the Black Holes. We analyse the implications of the First Law in a number of instructive cases, including that of the C-metric, and relate our findings to the previously obtained thermodynamics of slowly accelerating Black Holes in anti-de Sitter spacetime. The concept of thermodynamic length is found to be robust and a Christoudoulou-Ruffini formula for the C-metric is shown
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Connecting the Higgs Potential and Primordial Black Holes
'American Physical Society (APS)', 2020Co-Authors: Dai De-chang, Gregory Ruth, Stojkovic DejanAbstract:It was recently demonstrated that small small Black Holes can act as seeds for nucleating decay of the metastable Higgs vacuum, dramatically increasing the tunneling probability. Any primordial Black hole lighter than $4.5 \times 10^{14}$g at formation would have evaporated by now, and in the absence of new physics beyond the standard model, would therefore have entered the mass range in which seeded decay occurs, however, such true vacuum bubbles must percolate in order to completely destroy the false vacuum; this depends on the bubble number density and the rate of expansion of the universe. Here, we compute the fraction of the universe that has decayed to the true vacuum as a function of the formation temperature (or equivalently, mass) of the primordial Black Holes, and the spectral index of the fluctuations responsible for their formation. This allows us to constrain the mass spectrum of primordial Black Holes given a particular Higgs potential and conversely, should we discover primordial Black Holes of definite mass, we can constrain the Higgs potential parameters.Comment: 19 pages, 6 figures, accepted by PR
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Are 'Superentropic' Black Holes superentropic?
'Springer Science and Business Media LLC', 2020Co-Authors: Appels Michael, Cuspinera Leopoldo, Gregory Ruth, Krtouš Pavel, Kubizňák DavidAbstract:We study a critical limit in which asymptotically-AdS Black Holes develop maximal conical deficits and their horizons become non-compact. When applied to stationary rotating Black Holes this limit coincides with the “ultraspinning limit” and yields the Superentropic Black Holes whose entropy was derived recently and found to exceed the maximal possible bound imposed by the Reverse Isoperimetric Inequality [1, 2]. To gain more insight into this peculiar result, we study this limit in the context of accelerated AdS Black Holes that have unequal deficits along the polar axes, hence the maximal deficit need not appear on both poles simultaneously. Surprisingly, we find that in the presence of acceleration, the critical limit becomes smooth, and is obtained simply by taking various upper bounds in the parameter space that we elucidate. The Critical Black Holes thus obtained have many common features with Superentropic Black Holes, but are manifestly not superentropic. This raises a concern as to whether Superentropic Black Holes actually are superentropic.1 We argue that this may not be so and that the original conclusion is likely attributed to the degeneracy of the resulting first law
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Are Superentropic Black Holes superentropic?
'Springer Science and Business Media LLC', 2020Co-Authors: Appels Michael, Cuspinera Leopoldo, Gregory Ruth, Krtouš Pavel, Kubiznak DavidAbstract:We study a critical limit in which asymptotically-AdS Black Holes develop maximal conical deficits and their horizons become non-compact. When applied to stationary rotating Black Holes this limit coincides with the "ultraspinning limit" and yields the Superentropic Black Holes whose entropy was derived recently and found to exceed the maximal possible bound imposed by the Reverse Isoperimetric Inequality. To gain more insight into this peculiar result, we study this limit in the context of accelerated AdS Black Holes that have unequal deficits along the polar axes, hence the maximal deficit need not appear on both poles simultaneously. Surprisingly, we find that in the presence of acceleration, the critical limit becomes smooth, and is obtained simply by taking various upper bounds in the parameter space that we elucidate. The Critical Black Holes thus obtained have many common features with Superentropic Black Holes, but are manifestly not superentropic. This raises a concern as to whether Superentropic Black Holes actually are superentropic. We argue that this may not be so and that the original conclusion is likely attributed to the degeneracy of the resulting first law.Comment: 24 pages, 2 figures, version accepted by JHE
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Connecting the Higgs potential and primordial Black Holes.
'American Physical Society (APS)', 2020Co-Authors: Dai De-chang, Gregory Ruth, Stojkovic DejanAbstract:It was recently demonstrated that small Black Holes can act as seeds for nucleating decay of the metastable Higgs vacuum, dramatically increasing the tunneling probability. Any primordial Black hole lighter than 4.5 × 1014 g at formation would have evaporated by now, and in the absence of new physics beyond the standard model, would therefore have entered the mass range in which seeded decay occurs, however, such true vacuum bubbles must percolate in order to completely destroy the false vacuum; this depends on the bubble number density and the rate of expansion of the universe. Here, we compute the fraction of the universe that has decayed to the true vacuum as a function of the formation temperature (or equivalently, mass) of the primordial Black Holes, and the spectral index of the fluctuations responsible for their formation. This allows us to constrain the mass spectrum of primordial Black Holes given a particular Higgs potential and conversely, should we discover primordial Black Holes of definite mass, we can constrain the Higgs potential parameters
Zou De-cheng - One of the best experts on this subject based on the ideXlab platform.
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Scalarization of slowly rotating Black Holes
2021Co-Authors: Myung, Yun Soo, Zou De-chengAbstract:It is interesting to note that most Black Holes are born very slowly rotating. We investigate scalarization of slowly rotating Black Holes in the Einstein-scalar-Chern-Simons (EsCS) theory. In the slow rotation approximation, the CS term takes a linear form of rotation parameter $a$ which determines the tachyonic instability. The tachyonic instability for slowly rotating Black Holes represents the onset of spontaneous scalarization. It is shown that the slowly rotating Black Holes are unstable against a spherically symmetric scalar-mode perturbation for positive coupling $\alpha$, whereas these Black Holes are unstable for negative coupling without any $a$-bound.Comment: 12 pages, 3 figure
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Slowly rotating Black Holes and their scalarization
2021Co-Authors: Myung, Yun Soo, Zou De-chengAbstract:We study scalarization of slowly rotating Black Holes in the Einstein-scalar-Gauss-Bonnet (GB)-Chern-Simons (CS) theory. In the slow rotation approximation of $a\ll1$ with rotation parameter $a$, the GB term is given by a term for Schwarzschild Black hole, whereas the CS term takes a linear term of $a$. The tachyonic instability for slowly rotating Black Holes represents the onset of spontaneous scalarization. We use the (2+1)-dimensional hyperboloidal foliation method to show the tachyonic instability for slowly rotating Black Holes by considering the time evolution of a spherically symmetric scalar mode. A threshold (existence) curve is obtained from the constant scalar modes under time evolution, which means the boundary between stable and unstable Black Holes. It is found that the slowly rotating Black Holes turn out to be unstable against a spherically symmetric scalar-mode propagation for positive coupling $\alpha$. However, we could not find tachyonic instability and any $a$-bound for scalarization for negative coupling $\alpha$.Comment: 12 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:2103.0138
