9,118 research outputs found
Einstein-Gauss-Bonnet Black Strings at Large
We study the black string solutions in the Einstein-Gauss-Bonnet(EGB) theory
at large . By using the expansion in the near horizon region we derive
the effective equations that describe the dynamics of the EGB black strings.
The uniform and non-uniform black strings are obtained as the static solutions
of the effective equations. From the perturbation analysis of the effective
equations, we find that thin EGB black strings suffer from the Gregory-Laflamme
instablity and the GB term weakens the instability when the GB coefficient is
small, however, when the GB coefficient is large the GB term enhances the
instability. Furthermore, we numerically solve the effective equations to study
the non-linear instability. It turns out that the thin black strings are
unstable to developing inhomogeneities along their length, and at late times
they asymptote to the stable non-uniform black strings. The behavior is
qualitatively similar to the case in the Einstein gravity. Compared with the
black string instability in the Einstein gravity at large D, when the GB
coefficient is small the time needed to reach to final state increases, but
when the GB coefficient is large the time to reach to final state decreases.
Starting from the point of view in which the effective equations can be
interpreted as the equations for the dynamical fluid, we evaluate the transport
coefficients and find that the ratio of the shear viscosity and the entropy
density agrees with that obtained previously in the membrane paradigm after
taking the large limit.Comment: 22 pages, 8 figures, some errors corrected, references adde
Charged Scalar Perturbations around Garfinkle-Horowitz-Strominger Black Holes
We examine the stability of the Garfinkle-Horowitz-Strominger (GHS) black
hole under charged scalar perturbations. We find that different from the
neutral scalar field perturbations, only two numerical methods, such as the
continued fraction method and the asymptotic iteration method, can keep high
efficiency and accuracy requirements in the frequency domain computations. The
comparisons of the efficiency between these two methods have also been done.
Employing the appropriate numerical method, we show that the GHS black hole is
always stable against charged scalar perturbations. This is different from the
result obtained in the de Sitter and Anti-de Sitter black holes. Furthermore we
argue that in the GHS black hole background there is no amplification of the
incident charged scalar wave to cause the superradiance, so that the
superradiant instability cannot exist in this spacetime.Comment: 24 pages, 5 figure
Superradiant instability of Kerr-de Sitter black holes in scalar-tensor theory
We investigate in detail the mechanism of superradiance to render the
instability of Kerr-de Sitter black holes in scalar-tensor gravity. Our results
provide more clues to examine the scalar-tensor gravity in the astrophysical
black holes in the universe with cosmological constant. We also discuss the
spontaneous scalarization in the de Sitter background and find that this
instability can also happen in the spherical de Sitter configuration in a
special style.Comment: (v2)21 pages, 21 figures; Sec. V revised; This version has been
accepted for publication by JHE
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