1,302 research outputs found
Stability and Thermodynamics of AdS Black Holes with Scalar Hair
Recently a class of static spherical black hole solutions with scalar hair
was found in four and five dimensional gauged supergravity with modified, but
AdS invariant boundary conditions. These black holes are fully specified by a
single conserved charge, namely their mass, which acquires a contribution from
the scalar field. Here we report on a more detailed study of some of the
properties of these solutions. A thermodynamic analysis shows that in the
canonical ensemble the standard Schwarzschild-AdS black hole is stable against
decay into a hairy black hole. We also study the stability of the hairy black
holes and find there always exists an unstable radial fluctuation, in both four
and five dimensions. We argue, however, that Schwarzschild-AdS is probably not
the endstate of evolution under this instability.Comment: 18 pages, 4 figure
Violation of Energy Bounds in Designer Gravity
We continue our study of the stability of designer gravity theories, where
one considers anti-de Sitter gravity coupled to certain tachyonic scalars with
boundary conditions defined by a smooth function W. It has recently been argued
there is a lower bound on the conserved energy in terms of the global minimum
of W, if the scalar potential arises from a superpotential P and the scalar
reaches an extremum of P at infinity. We show, however, there are
superpotentials for which these bounds do not hold.Comment: 16 pages, 4 figures, v2: discussion of vacuum decay included, typos
corrected, reference adde
Particle Production near an AdS Crunch
We numerically study the dual field theory evolution of five-dimensional
asymptotically anti-de Sitter solutions of supergravity that develop
cosmological singularities. The dual theory is an unstable deformation of the N
= 4 gauge theory on R S3, and the big crunch singularity in the bulk
occurs when a boundary scalar field runs to infinity. Consistent quantum
evolution requires one imposes boundary conditions at infinity. Modeling these
by a steep regularization of the scalar potential, we find that when an
initially nearly homogeneous wavepacket rolls down the potential, most of the
potential energy of the initial configuration is converted into gradient energy
during the first oscillation of the field. This indicates there is no
transition from a big crunch to a big bang in the bulk for dual boundary
conditions of this kind.Comment: 20 pages, 6 figure
Holographic Description of AdS Cosmologies
To gain insight in the quantum nature of the big bang, we study the dual
field theory description of asymptotically anti-de Sitter solutions of
supergravity that have cosmological singularities. The dual theories do not
appear to have a stable ground state. One regularization of the theory causes
the cosmological singularities in the bulk to turn into giant black holes with
scalar hair. We interpret these hairy black holes in the dual field theory and
use them to compute a finite temperature effective potential. In our study of
the field theory evolution, we find no evidence for a "bounce" from a big
crunch to a big bang. Instead, it appears that the big bang is a rare
fluctuation from a generic equilibrium quantum gravity state.Comment: 34 pages, 8 figures, v2: minor changes, references adde
Further Holographic Investigations of Big Bang Singularities
We further explore the quantum dynamics near past cosmological singularities
in anisotropic Kasner-AdS solutions using gauge/gravity duality. The dual
description of the bulk evolution involves N=4 super Yang-Mills on the
contracting branch of an anisotropic de Sitter space and is well defined. We
compute two-point correlators of Yang-Mills operators of large dimensions using
spacelike geodesics anchored on the boundary. The correlator between two points
separated in a direction with negative Kasner exponent p always exhibits a pole
at horizon scales, in any dimension, which we interpret as a dual signature of
the classical bulk singularity. We find evidence that the pole is absent at
finite coupling in the dual field theory, indicating the singularity is
resolved.Comment: 26 pages, 3 figures. Version 3: added discussion on the validity of
the geodesic approximatio
Numerical simulation of a possible counterexample to cosmic censorship
A numerical simulation is presented here of the evolution of initial data of
the kind that was conjectured by Hertog, Horowitz and Maeda to be a violation
of cosmic censorship. That initial data is essentially a thick domain wall
connecting two regions of anti-deSitter space. The initial data has a free
parameter that is the initial size of the wall. The simulation shows no
violation of cosmic censorship, but rather the formation of a small black hole.
The simulation described here is for a moderate wall size and leaves open the
possibility that cosmic censorship might be violated for larger walls.Comment: discussion clarifie
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