316 research outputs found
Quasinormal modes for massless topological black holes
An exact expression for the quasinormal modes of scalar perturbations on a
massless topological black hole in four and higher dimensions is presented. The
massive scalar field is nonminimally coupled to the curvature, and the horizon
geometry is assumed to have a negative constant curvature.Comment: CECS style, 11 pages, no figures. References adde
Conserved Charges for Even Dimensional Asymptotically AdS Gravity Theories
Mass and other conserved Noether charges are discussed for solutions of
gravity theories with locally Anti-de Sitter asymptotics in 2n dimensions. The
action is supplemented with a boundary term whose purpose is to guarantee that
it reaches an extremum on the classical solutions, provided the spacetime is
locally AdS at the boundary. It is also shown that if spacetime is locally AdS
at spatial infinity, the conserved charges are finite and properly normalized
without requiring subtraction of a reference background. In this approach,
Noether charges associated to Lorentz and diffeomorphism invariance vanish
identically for constant curvature spacetimes. The case of zero cosmological
constant is obtained as a limit of AdS, where plays the role of a
regulator.Comment: 8 pages, RevTeX, no figures, two columns, references added and minor
typos corrected, final version for Phys. Rev.
Conserved charges for gravity with locally AdS asymptotics
A new formula for the conserved charges in 3+1 gravity for spacetimes with
local AdS asymptotic geometry is proposed. It is shown that requiring the
action to have an extremum for this class of asymptotia sets the boundary term
that must be added to the Lagrangian as the Euler density with a fixed weight
factor. The resulting action gives rise to the mass and angular momentum as
Noether charges associated to the asymptotic Killing vectors without requiring
specification of a reference background in order to have a convergent
expression. A consequence of this definition is that any negative constant
curvature spacetime has vanishing Noether charges. These results remain valid
in the limit of vanishing cosmological constant.Comment: 5 pages, 2 Columns, revtex. Last version for Phys. Rev. Let
Mass, Angular Momentum and Thermodynamics in Four-Dimensional Kerr-AdS Black Holes
In this paper, the connection between the Lorentz-covariant counterterms that
regularize the four-dimensional AdS gravity action and topological invariants
is explored. It is shown that demanding the spacetime to have a negative
constant curvature in the asymptotic region permits the explicit construction
of such series of boundary terms. The orthonormal frame is adapted to
appropriately describe the boundary geometry and, as a result, the boundary
term can be expressed as a functional of the boundary metric, extrinsic
curvature and intrinsic curvature. This choice also allows to write down the
background-independent Noether charges associated to asymptotic symmetries in
standard tensorial formalism. The absence of the Gibbons-Hawking term is a
consequence of an action principle based on a boundary condition different than
Dirichlet on the metric. This argument makes plausible the idea of regarding
this approach as an alternative regularization scheme for AdS gravity in all
even dimensions, different than the standard counterterms prescription. As an
illustration of the finiteness of the charges and the Euclidean action in this
framework, the conserved quantities and black hole entropy for four-dimensional
Kerr-AdS are computed.Comment: 15 pages,no figures,few references added,JHEP forma
Black hole mass and angular momentum in 2+1 gravity
We propose a new definition for the mass and angular momentum of neutral or
electrically charged black holes in 2+1 gravity with two Killing vectors. These
finite conserved quantities, associated with the SL(2,R) invariance of the
reduced mechanical system, are shown to be identical to the quasilocal
conserved quantities for an improved gravitational action corresponding to
mixed boundary conditions. They obey a general Smarr-like formula and, in all
cases investigated, are consistent with the first law of black hole
thermodynamics. Our framework is applied to the computation of the mass and
angular momentum of black hole solutions to several field-theoretical models.Comment: 23 pages, 3 references added, to be published in Physical Review
Determinant and Weyl anomaly of Dirac operator: a holographic derivation
We present a holographic formula relating functional determinants: the
fermion determinant in the one-loop effective action of bulk spinors in an
asymptotically locally AdS background, and the determinant of the two-point
function of the dual operator at the conformal boundary. The formula originates
from AdS/CFT heuristics that map a quantum contribution in the bulk partition
function to a subleading large-N contribution in the boundary partition
function. We use this holographic picture to address questions in spectral
theory and conformal geometry. As an instance, we compute the type-A Weyl
anomaly and the determinant of the iterated Dirac operator on round spheres,
express the latter in terms of Barnes' multiple gamma function and gain insight
into a conjecture by B\"ar and Schopka.Comment: 11 pages; new comments and references added, typos correcte
Black Hole Scan
Gravitation theories selected by requiring that they have a unique anti-de
Sitter vacuum with a fixed cosmological constant are studied. For a given
dimension d, the Lagrangians under consideration are labeled by an integer
k=1,2,...,[(d-1)/2]. Black holes for each d and k are found and are used to
rank these theories. A minimum possible size for a localized electrically
charged source is predicted in the whole set of theories, except General
Relativity. It is found that the thermodynamic behavior falls into two classes:
If d-2k=1, these solutions resemble the three dimensional black hole,
otherwise, their behavior is similar to the Schwarzschild-AdS_4 geometry.Comment: Two columns, revtex, 15 pages, 5 figures, minor typos corrected,
final version for Journa
A Note on Conserved Charges of Asymptotically Flat and Anti-de Sitter Spaces in Arbitrary Dimensions
The calculation of conserved charges of black holes is a rich problem, for
which many methods are known. Until recently, there was some controversy on the
proper definition of conserved charges in asymptotically anti-de Sitter (AdS)
spaces in arbitrary dimensions. This paper provides a systematic and explicit
Hamiltonian derivation of the energy and the angular momenta of both
asymptotically flat and asymptotically AdS spacetimes in any dimension D bigger
or equal to 4. This requires as a first step a precise determination of the
asymptotic conditions of the metric and of its conjugate momentum. These
conditions happen to be achieved in ellipsoidal coordinates adapted to the
rotating solutions.The asymptotic symmetry algebra is found to be isomorphic
either to the Poincare algebra or to the so(D-1, 2) algebra, as expected. In
the asymptotically flat case, the boundary conditions involve a generalization
of the parity conditions, introduced by Regge and Teitelboim, which are
necessary to make the angular momenta finite. The charges are explicitly
computed for Kerr and Kerr-AdS black holes for arbitrary D and they are shown
to be in agreement with thermodynamical arguments.Comment: 27 pages; v2 : references added, minor corrections; v3 : replaced to
match published version forthcoming in General Relativity and Gravitatio
Quasinormal modes for the SdS black hole : an analytical approximation scheme
Quasinormal modes for scalar field perturbations of a Schwarzschild-de Sitter
(SdS) black hole are investigated. An analytical approximation is proposed for
the problem. The quasinormal modes are evaluated for this approximate model in
the limit when black hole mass is much smaller than the radius of curvature of
the spacetime. The model mirrors some striking features observed in numerical
studies of time behaviour of scalar perturbations of the SdS black hole. In
particular, it shows the presence of two sets of modes relevant at two
different time scales, proportional to the surface gravities of the black hole
and cosmological horizons respectively. These quasinormal modes are not
complete - another feature observed in numerical studies. Refinements of this
model to yield more accurate quantitative agreement with numerical studies are
discussed. Further investigations of this model are outlined, which would
provide a valuable insight into time behaviour of perturbations in the SdS
spacetime.Comment: 12 pages, revtex, refs added and discussion expanded, version to
appear in Phys. Rev.
A Wormhole at the core of an infinite cosmic string
We study a solution of Einstein's equations that describes a straight cosmic
string with a variable angular deficit, starting with a deficit at the
core. We show that the coordinate singularity associated to this defect can be
interpreted as a traversible wormhole lodging at the the core of the string. A
negative energy density gradually decreases the angular deficit as the distance
from the core increases, ending, at radial infinity, in a Minkowski spacetime.
The negative energy density can be confined to a small transversal section of
the string by gluing to it an exterior Gott's like solution, that freezes the
angular deficit existing at the matching border. The equation of state of the
string is such that any massive particle may stay at rest anywhere in this
spacetime. In this sense this is 2+1 spacetime solution.Comment: 1 tex file and 5 eps files. To be Published in Nov. in Phys.Rev.
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