48 research outputs found
Asymptotic Quasinormal Modes of d-Dimensional Schwarzschild Black Hole with Gauss-Bonnet Correction
We obtain an analytic expression for the highly damped asymptotic quasinormal
mode frequencies of the -dimensional Schwarzschild black hole modified
by the Gauss-Bonnet term, which appears in string derived models of gravity.
The analytic expression is obtained under the string inspired assumption that
there exists a minimum length scale in the system and in the limit when the
coupling in front of the Gauss-Bonnet term in the action is small. Although
there are several similarities of this geometry with that of the Schwarzschild
black hole, the asymptotic quasinormal mode frequencies are quite different. In
particular, the real part of the asymptotic quasinormal frequencies for this
class of single horizon black holes in not proportional to log(3).Comment: 10 pages, latex file, changes in several equations, changes in the
abstract qualitative nature of conclusions unaffecte
Universal near-horizon conformal structure and black hole entropy
It is shown that a massless scalar probe reveals a universal near-horizon
conformal structure for a wide class of black holes, including the BTZ. The
central charge of the corresponding Virasoro algebra contains information about
the black hole. With a suitable quantization condition on the central charge,
the CFT associated with the black hole in our approach is consistent with the
recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT
framework has been identified with the construction of Frenkel, Lepowsky and
Meurman. This CFT admits the Fischer-Griess monster group as its symmetry. The
logarithm of the dimension of a specific representation of the monster group
has been identified by Witten as the entropy of the BTZ black hole. Our
algebraic approach shows that a wide class of black holes share the same
near-horizon conformal structure as that for the BTZ. With a suitable
quantization condition, the CFT's for all these black holes in our formalism
can be identified with the FLM model, although not through the AdS/CFT
correspondence. The corresponding entropy for the BTZ provides a lower bound
for the entropy of this entire class of black holes.Comment: References updated, text rearrange
A note on electromagnetic and gravitational perturbations of the Bardeen de Sitter black hole: quasinormal modes and greybody factors
Bardeen de-Sitter (BdS) black hole is a spherically symmetric solution of
Einstein's equation which is coupled to nonlinear electromagnetic field in a
way that one gets a regular solution, devoid of any singularity at the origin.
We compute the quasinormal (QN) frequencies for BdS black hole due to
electromagnetic and gravitational perturbations. We analyse the behaviour of
both real and imaginary parts of BdS QN frequencies by varying the black hole
parameters and compare frequencies with Reissner-Nordstr\"{o}m de-Sitter
(RN-dS) black hole. Interestingly, we find that the response of BdS and RN-dS
black holes under electromagnetic and gravitational perturbations are different
when the charge parameter is varied, which can be used to understand nonlinear
and linear electromagnetic fields in curved spacetime separately. A study on
the dynamics of perturbation as well as the scattering from the BdS black holes
using WKB approach is performed. Greybody factors and their variations with
black hole parameters are investigated.Comment: 21 pages, 38 figure