92 research outputs found
Quasinormal Modes and Stability Criterion of Dilatonic Black Hole in 1+1 and 4+1 Dimensions
We study the stability of black holes that are solutions of the dilaton
gravity derived from string-theoretical models in two and five dimensions
against to scalar field perturbations, using the Quasinormal Modes (QNMs)
approach. In order to find the QNMs corresponding to a black hole geometry, we
consider perturbations described by a massive scalar field non-minimally
coupled to gravity. We find that the QNM's frequencies turn out to be pure
imaginary leading to purely damped modes, that is in agreement with the
literature of dilatonic black holes. Our result exhibits the unstable behavior
of the considered geometry against the scalar perturbations. We consider both
the minimal coupling case, i.e., for which the coupling parameter
vanishes, and the case .Comment: sevarl changes, some reference was added, 10 pages, 4 figure
Exact Gravitational Quasinormal Frequencies of Topological Black Holes
We compute the exact gravitational quasinormal frequencies for massless
topological black holes in d-dimensional anti-de Sitter space. Using the gauge
invariant formalism for gravitational perturbations derived by Kodama and
Ishibashi, we show that in all cases the scalar, vector, and tensor modes can
be reduced to a simple scalar field equation. This equation is exactly solvable
in terms of hypergeometric functions, thus allowing an exact analytic
determination of the gravitational quasinormal frequencies.Comment: 14 pages, Latex; v2 additional reference
Bounding the greybody factors for Schwarzschild black holes
Greybody factors in black hole physics modify the naive Planckian spectrum
that is predicted for Hawking radiation when working in the limit of
geometrical optics. We consider the Schwarzschild geometry in (3+1) dimensions,
and analyze the Regge-Wheeler equation for arbitrary particle spin S and
wave-mode angular momentum L, deriving rigourous bounds on the greybody factors
as a function of S, L, wave frequency (omega), and the black hole mass, m.Comment: 5 pages; revtex4; V2 - two references adde
Dynamical evolution of a scalar field coupling to Einstein's tensor in the Reissner-Nordstr\"{o}m black hole spacetime
We study the dynamical evolution of a scalar field coupling to Einstein's
tensor in the background of Reissner-Nordstr\"{o}m black hole. Our results show
that the the coupling constant imprints in the wave dynamics of a scalar
perturbation. In the weak coupling, we find that with the increase of the
coupling constant the real parts of the fundamental quasinormal
frequencies decrease and the absolute values of imaginary parts increase for
fixed charge and multipole number . In the strong coupling, we find that
for the instability occurs when is larger than a certain
threshold value which deceases with the multipole number and
charge . However, for the lowest , we find that there does not exist
such a threshold value and the scalar field always decays for arbitrary
coupling constant.Comment: 11 pages, 6 figures, accepted for publication in Phys Rev
Quasinormal modes of black holes localized on the Randall-Sundrum 2-brane
We investigate conformal scalar, electromagnetic, and massless Dirac
quasinormal modes of a brane-localized black hole. The background solution is
the four-dimensional black hole on a 2-brane that has been constructed by
Emparan, Horowitz, and Myers in the context of a lower dimensional version of
the Randall-Sundrum model. The conformally transformed metric admits a Killing
tensor, allowing us to obtain separable field equations. We find that the
radial equations take the same form as in the four-dimensional "braneless"
Schwarzschild black hole. The angular equations are, however, different from
the standard ones, leading to a different prediction for quasinormal
frequencies.Comment: 10 pages, 7 figures; references added, version to appear in PR
Massive scalar field quasi-normal modes of higher dimensional black holes
We study quasinormal spectrum of massive scalar field in the -dimensional
black hole background. We found the qualitatively different dependence on the
field mass of the fundamental modes for . The behaviour of higher modes
is qualitatively the same for all . Thus for some particular values of mass
(of the field and of the black hole) the spectrum has two dominating
oscillations with a very long lifetime. Also we show that the asymptotically
high overtones do not depend on the field mass. In addition, we present the
generalisation of the Nollert improvement of the continued fraction technique
for the numerical calculation of quasi-normal frequencies of -dimensional
black holes.Comment: 8 pages, 4 figures, misprints corrected, version to appear in Phys.
Rev.
Gravitational instability of simply rotating AdS black holes in higher dimensions
We study the stability of AdS black hole holes rotating in a single two plane
for tensor-type gravitational perturbations in space-time dimensions.
First, by an analytic method, we show that there exists no unstable mode when
the magnitude of the angular momentum is smaller than where
is the horizon radius, and is the AdS curvature radius. Then, by numerical
calculations of quasinormal modes, using the separability of the relevant
perturbation equations, we show that an instability occurs for rapidly rotating
black holes with , although the growth rate is tiny (of order
of the inverse horizon radius). We give numerical evidences
indicating that this instability is caused by superradiance.Comment: 17 page
Quantum oscillations and black hole ringing
We show that strongly coupled field theories with holographic gravity duals
at finite charge density and low temperatures can undergo de Haas - van Alphen
quantum oscillations as a function of an external magnetic field. Exhibiting
this effect requires computation of the one loop contribution of charged bulk
fermions to the free energy. The one loop calculation is performed using a
formula expressing determinants in black hole backgrounds as sums over
quasinormal modes. At zero temperature, the periodic nonanalyticities in the
magnetic susceptibility as a function of the inverse magnetic field depend on
the low energy scaling behavior of fermionic operators in the field theory, and
are found to be softer than in weakly coupled theories. We also obtain
numerical and WKB results for the quasinormal modes of charged bosons in dyonic
black hole backgrounds, finding evidence for nontrivial periodic behavior as a
function of the magnetic field.Comment: 1+53 pages. 9 figures. v2: important changes to sections 3.4 - 3.6.
contribution of branch cut poles include
Quasi-Normal Modes of Brane-Localised Standard Model Fields II: Kerr Black Holes
This paper presents a comprehensive study of the fundamental quasinormal
modes of all Standard Model fields propagating on a brane embedded in a
higher-dimensional rotating black hole spacetime. The equations of motion for
fields with spin and 1 propagating in the induced-on-the-brane
background are solved numerically, and the dependence of their QN spectra on
the black hole angular momentum and dimensionality of spacetime is
investigated. It is found that the brane-localised field perturbations are
longer-lived when the higher-dimensional black hole rotates faster, while an
increase in the number of transverse-to-the-brane dimensions reduces their
lifetime. Finally, the quality factor , that determines the best oscillator
among the different field perturbations, is investigated and found to depend on
properties of both the particular field studied (spin, multipole numbers) and
the gravitational background (dimensionality, black hole angular momentum
number).Comment: 12 pages, 8 figures, typos corrected, version to appear in Phys. Rev.
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