23 research outputs found
Detection of gravitational waves from black holes: Is there a window for alternative theories?
Recently LIGO and VIRGO collaborations reported about observation of
gravitational-wave signal corresponding to the inspiral and merger of two black
holes, resulting into formation of the final black hole. It was shown that the
observations are consistent with the Einstein theory of gravity with high
accuracy limited mainly by the statistical error. Angular momentum and mass of
the final black hole were determined with rather large allowance of tens of
percents. Here we shall show that this indeterminacy in the range of the
black-hole parameters allows for some not negligible deformations of the Kerr
spacetime leading to the same frequencies of black-hole ringing. This means
that at the current precision of the experiment there remain some possibilities
for alternative theories of gravity.Comment: 5 pages, 1 figur
Quasinormal modes of the charged black hole in Gauss-Bonnet gravity
The d-dimensional string generated gravity models lead to Einstein-Maxwell
equations with quadratic order correction term called the Gauss-Bonnet term. We
calculate the quasinormal modes for the d-dimensional charged black hole in the
framework of this model. The quasinormal spectrum essentially depends upon the
Gauss-Bonnet coupling parameter which is related to the string scale,
and is totally different from that for black holes derived from Einstein
action. In particular, at large the quasinormal modes are proportional
to , while as goes to zero the qusinormal modes approach their
Schwarzschild values. In contrary to Einstein theory black hole behavior, the
damping rate of the charged GB black hole as a function of charge does not
contain a chracteristic maximum, but instead the monotonic falling down is
observed. In addition, there have been obtained an asymptotic formula for large
multipole numbers.Comment: 16 pages, 4 figures, 3 tables; misprints correcte
Quasinormal frequencies of Schwarzschild black holes in anti-de Sitter spacetimes: A complete study on the asymptotic behavior
We present a thorough analysis for the quasinormal (QN) behavior, associated
with the decay of scalar, electromagnetic and gravitational perturbations, of
Schwarzschild-anti-de Sitter black holes. As it is known the anti-de Sitter
(AdS) QN spectrum crucially depends on the relative size of the black hole to
the AdS radius. There are three different types of behavior depending on
whether the black hole is large, intermediate, or small. The results of
previous works, concerning lower overtones for large black holes, are completed
here by obtaining higher overtones for all the three black hole regimes. There
are two major conclusions that one can draw from this work: First,
asymptotically for high overtones, all the modes are evenly spaced, and this
holds for all three types of regime, large, intermediate and small black holes,
independently of l, where l is the quantum number characterizing the angular
distribution; Second, the spacing between modes is apparently universal, in
that it does not depend on the field, i.e., scalar, electromagnetic and
gravitational QN modes all have the same spacing for high overtones. We are
also able to prove why scalar and gravitational perturbations are isospectral,
asymptotically for high overtones, by introducing appropriate superpartner
potentials.Comment: 22 page