Recent work indicates that the strong cosmic censorship hypothesis is violated by nearly extremal Reissner–Nordström–de Sitter black holes. It was argued that perturbations of such a black hole decay ...sufficiently rapidly that the perturbed spacetime can be extended across the Cauchy horizon as a weak solution of the equations of motion. In this paper we consider the case of Kerr–de Sitter black holes. We find that, for any nonextremal value of the black hole parameters, there are quasinormal modes which decay sufficiently slowly to ensure that strong cosmic censorship is respected. Our analysis covers both scalar field and linearized gravitational perturbations.
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It has been argued that the strong cosmic censorship conjecture is violated by Reissner-Nordström-de Sitter black holes: for near-extremal black holes, generic scalar field perturbations ...arising from smooth initial data have finite energy at the Cauchy horizon even though they are not continuously differentiable there. In this paper, we consider the analogous problem for coupled gravitational and electromagnetic perturbations. We find that such perturbations exhibit a much worse violation of strong cosmic censorship: for a sufficiently large near-extremal black hole, perturbations arising from smooth initial data can be extended through the Cauchy horizon in an arbitrarily smooth way. This is in apparent contradiction with an old argument in favour of strong cosmic censorship. We resolve this contradiction by showing that this old argument is valid only for initial data that is not smooth. This is in agreement with the recent proposal that, to recover strong cosmic censorship, one must allow rough initial data.
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We investigate the stability of the inner horizon of a rotating BTZ black hole. We show that linear perturbations arising from smooth initial data are arbitrarily differentiable at the ...inner horizon if the black hole is sufficiently close to extremality. This is demonstrated for scalar fields, for massive Chern-Simons fields, for Proca fields, and for massive spin-2 fields. Thus the strong cosmic censorship conjecture is violated by a near-extremal BTZ black hole in a large class of theories. However, we show that a weaker \rough" version of the conjecture is respected. We calculate the renormalized energymomentum tensor of a scalar field in the Hartle-Hawking state in the BTZ geometry. We show that the result is finite at the inner horizon of a near-extremal black hole. Hence the backreaction of vacuum polarization does not enforce strong cosmic censorship.
We find hairy black holes of Einstein-Maxwell theory with a complex scalar field that is confined inside a box in a Minkowski background. These regular hairy black holes are asymptotically flat, and ...thus the presence of the box or mirror allows us to evade well-known no-hair theorems. We also find the Israel surface stress tensor that the confining box must have to obey the energy conditions. In the zero horizon radius limit, these hairy black holes reduce to a regular asymptotically flat hairy soliton. We find our solutions using perturbation theory. At leading order, a hairy black hole can be seen as a Reissner-Nordstrom black hole placed on top of a hairy soliton with the same chemical potential (so that the system is in thermodynamic equilibrium). The hairy black holes merge with the Reissner-Nordstrom black hole family at the onset of the superradiant instability. When they coexist, for a given energy and electric charge, hairy black holes have higher entropy than caged Reissner-Nordstrom black holes. Therefore, our hairy black holes are the natural candidates for the end point of charged superradiance in the Reissner-Nordstrom black hole mirror system.
We give strong numerical evidence for the existence of an instability afflicting six-dimensional Reissner-Nordström de Sitter (RNdS) black holes. This instability is akin of the Konoplya-Zhidenko ...instability present in RNdS black holes in seven spacetime dimensions and above. Moreover, we perform a detailed analysis of the near-horizon limit of extremal RNdS black holes, and find that, typically, unstable gravitational modes effectively behave as a massive scalar field whose mass violates the AdS2 Breitenlöhner-Freedman bound (if and only if d ≥ 6 ), thus providing a physical argument for the existence of the instability. Finally, we show that the frequency spectrum of perturbations of RNdS has a remarkable intricate structure with several bifurcations/mergers that appears unique to RNdS black holes.
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The existence of phase-separated states is an essential feature of infinite-volume systems with a thermal, first-order phase transition. At energies between those at which the phase ...transition takes place, equilibrium homogeneous states are either metastable or suffer from a spinodal instability. In this range the stable states are inhomogeneous, phase-separated states. We use holography to investigate how this picture is modified at finite volume in a strongly coupled, four-dimensional gauge theory. We work in the planar limit,
N → ∞
, which ensures that we remain in the thermodynamic limit. We uncover a rich set of inhomogeneous states dual to lumpy black branes on the gravity side, as well as first- and second-order phase transitions between them. We establish their local (in)stability properties and show that fully non-linear time evolution in the bulk takes unstable states to stable ones.
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We consider the static charged black hole bomb system, originally designed for a (uncharged) rotating superradiant system by Press and Teukolsky. A charged scalar field confined in a ...Minkowski cavity with a Maxwell gauge field has a quantized spectrum of normal modes that can fit inside the box. Back-reacting non-linearly these normal modes, we find the hairy solitons, a.k.a boson stars (depending on the chosen U(1) gauge), of the theory. The scalar condensate is totally confined inside the box and, outside it, we have the Reissner-Nordström solution. The Israel junction conditions at the box surface layer determine the stress tensor that the box must have to confine the scalar hair. Some of these horizonless hairy solutions exist for any value of the scalar field charge and not only above the natural critical charges of the theory (namely, the critical charges for the onset of the near-horizon and superradiant instabilities of the Reissner-Nordström black hole). However, the ground state solutions have a non-trivial intricate phase diagram with a main and a secondary family of solitons (some with a Chandrasekhar mass limit but others without) and there are a third and a fourth critical scalar field charges where the soliton spectra changes radically. Most of these intricate properties are not captured by a higher order perturbative analysis of the problem where we simply back-react a normal mode of the system.
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We find the phase diagram of solutions of the charged black hole bomb system. In particular, we find the static hairy black holes of Einstein-Maxwell-Scalar theory confined in a Minkowski ...box. We impose boundary conditions such that the scalar field vanishes at and outside a cavity of constant radius. These hairy black holes are asymptotically flat with a scalar condensate floating above the horizon. We identify four critical scalar charges which mark significant changes in the qualitative features of the phase diagram. When they coexist, hairy black holes always have higher entropy than the Reissner-Nordström black hole with the same quasilocal mass and charge. So hairy black holes are natural candidates for the endpoint of the superradiant/near-horizon instabilities of the black hole bomb system. We also relate hairy black holes to the boson stars of the theory. When it has a zero horizon radius limit, the hairy black hole family terminates on the boson star family. Finally, we find the Israel surface tensor of the box required to confine the scalar condensate and that it can obey suitable energy conditions.
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