13,798 research outputs found
Effective Conformal Descriptions of Black Hole Entropy
It is no longer considered surprising that black holes have temperatures and
entropies. What remains surprising, though, is the universality of these
thermodynamic properties: their exceptionally simple and general form, and the
fact that they can be derived from many very different descriptions of the
underlying microscopic degrees of freedom. I review the proposal that this
universality arises from an approximate conformal symmetry, which permits an
effective "conformal dual" description that is largely independent of the
microscopic details.Comment: 27 pages; solicited review article, to appear in Entrop
Hamiltonian evolution and quantization for extremal black holes
We present and contrast two distinct ways of including extremal black holes
in a Lorentzian Hamiltonian quantization of spherically symmetric
Einstein-Maxwell theory. First, we formulate the classical Hamiltonian dynamics
with boundary conditions appropriate for extremal black holes only. The
Hamiltonian contains no surface term at the internal infinity, for reasons
related to the vanishing of the extremal hole surface gravity, and quantization
yields a vanishing black hole entropy. Second, we give a Hamiltonian
quantization that incorporates extremal black holes as a limiting case of
nonextremal ones, and examine the classical limit in terms of wave packets. The
spreading of the packets, even the ones centered about extremal black holes, is
consistent with continuity of the entropy in the extremal limit, and thus with
the Bekenstein-Hawking entropy even for the extremal holes. The discussion
takes place throughout within Lorentz-signature spacetimes.Comment: 16 pages, LaTeX using REVTeX v3.1. (v2: Reference added.
Non-uniqueness, Counterrotation, and Negative Horizon Mass of Einstein-Maxwell-Chern-Simons Black Holes
Stationary black holes in 5-dimensional Einstein-Maxwell-Chern-Simons theory
possess surprising properties. When considering the Chern-Simons coefficient
as a parameter, two critical values of appear: the
supergravity value , and the value . At
, supersymmetric black holes with vanishing horizon angular
velocity, but finite angular momentum exist. As increases beyond
a rotational instability arises, and counterrotating black
holes appear, whose horizon rotates in the opposite sense to the angular
momentum. Thus supersymmetry is associated with the borderline between
stability and instability. At rotating black holes with vanishing
angular momentum emerge. Beyond black holes may possess a negative
horizon mass, while their total mass is positive. Charged rotating black holes
with vanishing gyromagnetic ratio appear, and black holes are no longer
uniquely characterized by their global charges.Comment: 15 pages, 16 figures, MPLA style, invited review for Modern Physics
Letters
Negative Horizon Mass for Rotating Black Holes
Charged rotating black holes of Einstein-Maxwell-Chern-Simons theory in odd
dimensions, , may possess a negative horizon mass, while their total
mass is positive. This surprising feature is related to the existence of
counterrotating solutions, where the horizon angular velocity and the
angular momentum possess opposite signs. Black holes may further possess
vanishing horizon angular velocity while they have finite angular momentum, or
they may possess finite horizon angular velocity while their angular momentum
vanishes. In D=9 even non-static black holes with appear. Charged
rotating black holes with vanishing gyromagnetic ratio exist, and black holes
need no longer be uniquely characterized by their global charges.Comment: 17 pages, 16 figure
Pair production of scalars around near-extremal Kerr-Sen black holes
We investigate the charged scalar pair production near the horizon of a
near-extremal Kerr-Sen black holes. The condition for pair production to occur
has relation to the violation of Breitenlohner-Freedman bound in an AdS
space. The method employed in this work has been used to show the pair
production in the near-horizon of a near-extremal Kerr-Newman black hole and
its non-rotating case as well. We also discuss the static limit of our result.Comment: 16 pages, 1 figur
The Quantum Physics of Black Holes: Results from String Theory
We review recent progress in our understanding of the physics of black holes.
In particular, we discuss the ideas from string theory that explain the entropy
of black holes from a counting of microstates of the hole, and the related
derivation of unitary Hawking radiation from such holes.Comment: 49 pages, Latex, 4 figures, (Review article
Zero Temperature Limit of Holographic Superconductors
We consider holographic superconductors whose bulk description consists of
gravity minimally coupled to a Maxwell field and charged scalar field with
general potential. We give an analytic argument that there is no "hard gap":
the real part of the conductivity at low frequency remains nonzero (although
typically exponentially small) even at zero temperature. We also numerically
construct the gravitational dual of the ground state of some holographic
superconductors. Depending on the charge and dimension of the condensate, the
infrared theory can have emergent conformal or just Poincare symmetry. In all
cases studied, the area of the horizon of the dual black hole goes to zero in
the extremal limit, consistent with a nondegenerate ground state.Comment: 27 pages, 8 figure
An Inhomogeneous Transference Principle and Diophantine Approximation
In a landmark paper, D.Y. Kleinbock and G.A. Margulis established the
fundamental Baker-Sprindzuk conjecture on homogeneous Diophantine approximation
on manifolds. Subsequently, there has been dramatic progress in this area of
research. However, the techniques developed to date do not seem to be
applicable to inhomogeneous approximation. Consequently, the theory of
inhomogeneous Diophantine approximation on manifolds remains essentially
non-existent.
In this paper we develop an approach that enables us to transfer homogeneous
statements to inhomogeneous ones. This is rather surprising as the
inhomogeneous theory contains the homogeneous theory and so is more general. As
a consequence, we establish the inhomogeneous analogue of the Baker-Sprindzuk
conjecture. Furthermore, we prove a complete inhomogeneous version of the
profound theorem of Kleinbock, Lindenstrauss & Weiss on the extremality of
friendly measures. The results obtained in this paper constitute the first step
towards developing a coherent inhomogeneous theory for manifolds in line with
the homogeneous theory.Comment: 37 pages: a final section on further developments has been adde
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