129 research outputs found
Quasinormal modes of black holes immersed in a strong magnetic field
We found quasinormal modes, both in time and frequency domains, of the Ernst
black holes, that is neutral black holes immersed in an external magnetic
field. The Ernst solution reduces to the Schwarzschild solution, when the
magnetic field vanishes. It is found that the quasinormal spectrum for massless
scalar field in the vicinity of the magnetized black holes acquires an
effective "mass" , where m is the azimuthal number and B is
parameter describing the magnetic field. We shall show that in the presence of
a magnetic field quasinormal modes are longer lived and have larger oscillation
frequencies. The perturbations of higher dimensional magnetized black holes by
Ortaggio and of magnetized dilaton black holes by Radu are considered.Comment: 5 pages, RevTe
Decay of massive scalar field in a Schwarzschild background
The decay of massive scalar field in the Schwarzschild black hole background
is investigated here by consideration its quasinormal spectrum. It has been
proved that the so-called modes, which are arbitrary long
living (purely real) modes, can exist only if the effective potential is not
zero at least at one of the boundaries of the -region. We have observed that
the quasinormal spectrum exists for all field masses and proved both
analytically and numerically that when the real part of the
frequencies approaches the same asymptotical value () as in the
case of the massless field.Comment: 8 pages, 3 figures, Physics Letters B, at pres
Massive charged scalar field in a Reissner-Nordstrom black hole background: quasinormal ringing
We compute characteristic (quasinormal) frequencies corresponding to decay of
a massive charged scalar field in a Reissner-Nordstrom black hole background.
It proves that, contrary to the behavior at very late times, at the stage of
quasinormal ringing the neutral perturbations will damp slower than the charged
ones. In the limit of the extremal black hole the damping rate of charged and
neutral perturbations coincides. Possible connection of this with the critical
collapse in a massive scalar electrodynamics is discussed.Comment: 7 pages, LaTeX, 6 figure
Gravitational quasinormal radiation of higher-dimensional black holes
We find the gravitational resonance (quasinormal) modes of the higher
dimensional Schwarzschild and Reissner-Nordstrem black holes. The effect on the
quasinormal behavior due to the presence of the term is investigated.
The QN spectrum is totally different for different signs of . In more
than four dimensions there excited three types of gravitational modes: scalar,
vector, and tensor. They produce three different quasinormal spectra, thus the
isospectrality between scalar and vector perturbations, which takes place for
D=4 Schwarzschild and Schwarzschild-de-Sitter black holes, is broken in higher
dimensions. That is the scalar-type gravitational perturbations, connected with
deformations of the black hole horizon, which damp most slowly and therefore
dominate during late time of the black hole ringing.Comment: 13 pages, 2 figures, several references are adde
Gravitational spectrum of black holes in the Einstein-Aether theory
Evolution of gravitational perturbations, both in time and frequency domains,
is considered for a spherically symmetric black hole in the non-reduced
Einstein-Aether theory. It is shown that real oscillation frequency and damping
rate are larger for the Einstein-Aether black hole than for the Schwarzschild
black hole. This may provide an opportunity to observe aether in the
forthcoming experiments with new generation of gravitational antennas.Comment: 4 pages, RevTex, to be published in Phys. Lett.
Perturbations and quasi-normal modes of black holes in Einstein-Aether theory
We develop a new method for calculation of quasi-normal modes of black holes,
when the effective potential, which governs black hole perturbations, is known
only numerically in some region near the black hole. This method can be applied
to perturbations of a wide class of numerical black hole solutions. We apply it
to the black holes in the Einstein-Aether theory, a theory where general
relativity is coupled to a unit time-like vector field, in order to observe
local Lorentz symmetry violation. We found that in the non-reduced
Einstein-Aether theory, real oscillation frequency and damping rate of
quasi-normal modes are larger than those of Schwarzschild black holes in the
Einstein theory.Comment: 6 pages, 3 figures, RevTex, to be published in Phys. Lett.
Stability of multidimensional black holes: complete numerical analysis
We analyze evolution of gravitational perturbations of D-dimensional
Schwarzschild, Reissner-Nordstr\"om, and Reissner-Nordstrom-de Sitter black
holes. It is known that the effective potential for the scalar type of
gravitational perturbations has negative gap near the event horizon. This gap,
for some values of the parameters Q (charge), Lambda (cosmological constant)
and D (number of space-time dimensions), cannot be removed by S-deformations.
Thereby, there is no proof of (in)stability for those cases. In the present
paper, by an extensive search of quasinormal modes, both in time and frequency
domains, we shall show that spherically symmetric static black holes with
arbitrary charge and positive (de Sitter) lambda-term are stable for D=5, 6,
>...11. In addition, we give a complete numerical data for all three types
(scalar, vector and tensor) of gravitational perturbations for
multi-dimensional black holes with charge and Lambda-term. The influence of
charge, Lambda-term and number of extra dimensions on black hole quasinormal
spectrum is discussed.Comment: 12 pages, RevTe
Quasinormal behavior of the D-dimensional Schwarzshild black hole and higher order WKB approach
We study characteristic (quasinormal) modes of a -dimensional Schwarzshild
black hole. It proves out that the real parts of the complex quasinormal modes,
representing the real oscillation frequencies, are proportional to the product
of the number of dimensions and inverse horizon radius . The
asymptotic formula for large multipole number and arbitrary is derived.
In addition the WKB formula for computing QN modes, developed to the 3rd order
beyond the eikonal approximation, is extended to the 6th order here. This gives
us an accurate and economic way to compute quasinormal frequencies.Comment: 15 pages, 6 figures, the 6th order WKB formula for computing QNMs in
Mathematica is available from https://goo.gl/nykYG
Holographic conductivity of zero temperature superconductors
Using the recently found by G. Horowitz and M. Roberts (arXiv:0908.3677)
numerical model of the ground state of holographic superconductors (at zero
temperature), we calculate the conductivity for such models. The universal
relation connecting conductivity with the reflection coefficient was used for
finding the conductivity by the WKB approach. The dependence of the
conductivity on the frequency and charge density is discussed. Numerical
calculations confirm the general arguments of (arXiv:0908.3677) in favor of
non-zero conductivity even at zero temperature. In addition to the
Horowitz-Roberts solution we have found (probably infinite) set of extra
solutions which are normalizable and reach the same correct RN-AdS asymptotic
at spatial infinity. These extra solutions (which correspond to larger values
of the grand canonical potential) lead to effective potentials that also vanish
at the horizon and thus correspond to a non-zero conductivity at zero
temperature.Comment: 9 pages, 10 figure
Area Spectrum of Extremal Reissner-Nordstr\"om Black Holes from Quasi-normal Modes
Using the quasi-normal modes frequency of extremal Reissner-Nordstr\"om black
holes, we obtain area spectrum for these type of black holes. We show that the
area and entropy black hole horizon are equally spaced. Our results for the
spacing of the area spectrum differ from that of schwarzschild black holes.Comment: 6 pages, no figure, accepted for publication in Phys. Rev.
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