No Arabic abstract
Recently, it has been found that, with the Renyi statistics, the asymptotically flat Schwarzschild black hole can be in thermal equilibrium with infinite heat reservior at a fixed temperature when its event horizon radius is larger than the characteristic length scale $L_lambda=1/sqrt{pi lambda}$, where $lambda$ is the nonextensivity parameter. In the Renyi extended phase space with the $PdV$ work term, an off-shell free energy in the canonical ensemble with the thermodynamic volume as an order parameter is considered to identify a first-order Hawking-Page (HP) phase transition as a solid/liquid phase transition. It has the latent heat of fusion from solid (corresponding to thermal radiation) to liquid (corresponding to black hole) in the form of $sim 1/sqrt{lambda}$; this is evident of the absence of the HP phase transition in the case of asymptotically flat Schwarzschild black hole from the GB statistics ($lambda=0$). Moreover, we investigate the generalized second law of black hole thermodynamics (GSL) in Renyi statistics by considering the black hole as a working substance in heat engine. Interestingly, an efficiency $eta$ of the black hole in a Carnot cycle takes the form $eta_c=1-T_text{C}/T_text{H}$. This confirms the validity of the GSL in the Renyi extended phase space.
The phase structure and critical phenomena of the 3+1 dimensional charged black holes in asymptotically flat spacetime are investigated in terms of thermodynamic properties within the Renyi statistics. With this approach as the non-extensive parameter above zero, we find that the charged black hole can be in thermodynamic equilibrium with surrounding thermal radiation, and have a Hawking-Page phase transition in the same way in the case of AdS charged black hole. This gives more evidence supporting the proposal that there exists an equivalence between the black hole thermodynamics in asymptotically flat spacetime via Renyi statistics and that in asymptotically AdS spacetime via Gibbs-Boltzmann statistics, proposed by Czinner et al. However, the present work also provides another aspect of supporting evidence through exploring the extended phase space within the Renyi statistics. Working on a modified version of Smarr formula, the thermodynamic pressure $P$ and volume $v$ of a charged black hole are found to be related to the non-extensive parameter. The resulting $P-v$ diagram indicates that the thermodynamics of charged black holes in asymptotically flat spacetime via Renyi statistics has the Van der Waals phase structure, equivalent to that in asymptotically AdS spacetime via Gibbs-Boltzmann statistics.
We argue that a convenient way to analyze instabilities of black holes in AdS space is via Bragg-Williams construction of a free energy function. Starting with a pedagogical review of this construction in condensed matter systems and also its implementation to Hawking-Page transition, we study instabilities associated with hairy black holes and also with the $R$-charged black holes. For the hairy black holes, an analysis of thermal quench is presented.
One of the problems in the current asymptotic symmetry would be to extend the black hole to the rotating one. Therefore, in this paper, we obtain a four-dimensional asymptotically flat rotating black hole solution including the supertraslation corrections.
Asymptotically flat black holes in $2+1$ dimensions are a rarity. We study the recently found black flower solutions (asymptotically flat black holes with deformed horizons), static black holes, rotating black holes and the dynamical black flowers (black holes with radiative gravitons ) of the purely quadratic version of new massive gravity. We show how they appear in this theory and we also show that they are also solutions to the infinite order extended version of the new massive gravity, that is the Born-Infeld extension of new massive gravity with an amputated Einsteinian piece. The same metrics also solve the topologically extend
We study asymptotically flat black holes with massive graviton hair within the ghost-free bigravity theory. There have been contradictory statements in the literature about their existence -- such solutions were reported some time ago, but later a different group claimed the Schwarzschild solution to be the only asymptotically flat black hole in the theory. As a result, the controversy emerged. We have analyzed the issue ourselves and have been able to construct such solutions within a carefully designed numerical scheme. We find that for given parameter values there can be one or two asymptotically flat hairy black holes in addition to the Schwarzschild solution. We analyze their perturbative stability and find that they can be stable or unstable, depending on the parameter values. The masses of stable hairy black holes that would be physically relevant range form stellar values up to values typical for supermassive black holes. One of their two metrics is extremely close to Schwarzschild, while all their hair is hidden in the second metric that is not coupled to matter and not directly seen. If the massive bigravity theory indeed describes physics, the hair of such black holes should manifest themselves in violent processes like black hole collisions and should be visible in the structure of the signals detected by LIGO/VIRGO.