56 research outputs found
Thermodynamic Properties of Small Localized Black Holes
In a previous paper, we developed a numerical method to obtain a static black
hole localized on a 3-brane in the Randall-Sundrum infinite braneworld, and
presented examples of numerical solutions that describe small localized black
holes. In this paper we quantitatively analyze the behavior of the numerically
obtained black hole solutions, focusing on thermodynamic quantities. The
thermodynamic relations show that the localized black hole deviates smoothly
from a five-dimensional Schwarzschild black hole, which is a solution in the
limit of a small horizon radius. We compare the thermodynamic behavior of these
solutions with that of the exact solution on the 2-brane in the 4D braneworld.
We find similarities between them.Comment: 6 pages, 6 figures, RevTex, references adde
Properties of Kaluza-Klein black holes
We detail numerical methods to compute the geometry of static vacuum black
holes in 6 dimensional gravity compactified on a circle. We calculate
properties of these Kaluza-Klein black holes for varying mass, while keeping
the asymptotic compactification radius fixed. For increasing mass the horizon
deforms to a prolate ellipsoid, and the geometry near the horizon and axis
decompactifies. We are able to find solutions with horizon radii approximately
equal to the asymptotic compactification radius. Having chosen 6-dimensions, we
may compare these solutions to the non-uniform strings compactified on the same
radius of circle found in previous numerical work. We find the black holes
achieve larger masses and horizon volumes than the most non-uniform strings.
This sheds doubt on whether these solution branches can merge via a topology
changing solution. Further work is required to resolve whether there is a
maximum mass for the black holes, or whether the mass can become arbitrarily
large.Comment: 33 pages, 13 colour figures; v2 minor corrections and some figures
beautifie
Second order perturbations in the radius stabilized Randall-Sundrum two branes model II -- Effect of relaxing strong coupling approximation --
We discuss gravitational perturbations in the Randall-Sundrum two branes
model with radius stabilization. Following the idea by Goldberger and Wise for
the radius stabilization, we introduce a scalar field which has potentials
localized on the branes in addition to a bulk potential. In our previous paper
we discussed gravitational perturbations induced by static, spherically
symmetric and nonrelativistic matter distribution on the branes under the
condition that the values of the scalar field on the respective branes cannot
fluctuate due to its extremely narrow brane potentials. We call this case the
strong coupling limit. Our concern in this paper is to generalize our previous
analysis relaxing the limitation of taking the strong coupling limit. We find
that new corrections in metric perturbations due to relaxing the strong
coupling limit enhance the deviation from the 4D Einstein gravity only in some
exceptional cases. In the case that matter fields reside on the negative
tension brane, the stabilized radion mass becomes very small when the new
correction becomes large.Comment: 12 pages, No figures, typos correcte
Probing anisotropies of gravitational-wave backgrounds with a space-based interferometer: geometric properties of antenna patterns and their angular power
We discuss the sensitivity to anisotropies of stochastic gravitational-wave
backgrounds (GWBs) observed via space-based interferometer. In addition to the
unresolved galactic binaries as the most promising GWB source of the planned
Laser Interferometer Space Antenna (LISA), the extragalactic sources for GWBs
might be detected in the future space missions. The anisotropies of the GWBs
thus play a crucial role to discriminate various components of the GWBs. We
study general features of antenna pattern sensitivity to the anisotropies of
GWBs beyond the low-frequency approximation. We show that the sensitivity of
space-based interferometer to GWBs is severely restricted by the data
combinations and the symmetries of the detector configuration. The spherical
harmonic analysis of the antenna pattern functions reveals that the angular
power of the detector response increases with frequency and the detectable
multipole moments with effective sensitivity h_{eff} \sim 10^{-20} Hz^{-1/2}
may reach 8-10 at mHz in the case of the single
LISA detector. However, the cross correlation of optimal interferometric
variables is blind to the monopole (\ell=0) intensity anisotropy, and also to
the dipole (\ell=1) in some case, irrespective of the frequency band. Besides,
all the self-correlated signals are shown to be blind to the odd multipole
moments (\ell=odd), independently of the frequency band.Comment: RevTex4, 22 pages, 6 figures (low resolution), typos correcte
Doubly Spinning Black Rings
We study a method to solve stationary axisymmetric vacuum Einstein equations
numerically. As an illustration, the five-dimensional doubly spinning black
rings that have two independent angular momenta are formulated in a way
suitable for fully nonlinear numerical method. Expanding for small second
angular velocity, the formulation is solved perturbatively upto second order
involving the backreaction from the second spin. The obtained solutions are
regular without conical singularity, and the physical properties are discussed
with the phase diagram of the reduced entropy vs the reduced angular momenta.
Possible extensions of the present approach to constructing the higher
dimensional version of black ring and the ring with the cosmological constant
are also discussed.Comment: 20 pages, 6 figure
Origin of black string instability
It is argued that many nonextremal black branes exhibit a classical
Gregory-Laflamme (GL) instability. Why does the universal instability exist? To
find an answer to this question and explore other possible instabilities, we
study stability of black strings for all possible types of gravitational
perturbation. The perturbations are classified into tensor-, vector-, and
scalar-types, according to their behavior on the spherical section of the
background metric. The vector and scalar perturbations have exceptional
multipole moments, and we have paid particular attention to them. It is shown
that for each type of perturbations there is no normalizable negative
(unstable) modes, apart from the exceptional mode known as s-wave perturbation
which is exactly the GL mode. We discuss the origin of instability and comment
on the implication for the correlated-stability conjecture.Comment: 19 pages (revtex4), 4 figures; references added, minor correction
Detecting a gravitational-wave background with next-generation space interferometers
Future missions of gravitational-wave astronomy will be operated by
space-based interferometers, covering very wide range of frequency. Search for
stochastic gravitational-wave backgrounds (GWBs) is one of the main targets for
such missions, and we here discuss the prospects for direct measurement of
isotropic and anisotropic components of (primordial) GWBs around the frequency
0.1-10 Hz. After extending the theoretical basis for correlation analysis, we
evaluate the sensitivity and the signal-to-noise ratio for the proposed future
space interferometer missions, like Big-Bang Observer (BBO), Deci-Hertz
Interferometer Gravitational-wave Observer (DECIGO) and recently proposed
Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at
low frequency may be a big obstacle and significantly reduce the
signal-to-noise ratio of GWBs. As a result, minimum detectable amplitude may
reach h^2 \ogw = 10^{-15} \sim 10^{-16}, as long as foreground point sources
are properly subtracted. Based on correlation analysis, we also discuss
measurement of anisotropies of GWBs. As an example, the sensitivity level
required for detecting the dipole moment of GWB induced by the proper motion of
our local system is closely examined.Comment: 19 pages, 6 figures, references added, typos correcte
Dynamics of colliding branes and black brane production
We study the dynamics of colliding domain walls including self-gravity. The
initial data is set up by applying a BPS domain wall in five-dimensional
supergravity, and we evolve the system determining the final outcome of
collisions. After a collision, a spacelike curvature singularity covered by a
horizon is formed in the bulk, resulting in a black brane with trapped domain
walls. This is a generic consequence of collisions, except for non-relativistic
weak field cases, in which the walls pass through one another or multiple
bounces take place without singularity formation. These results show that
incorporating the self-gravity drastically changes a naive picture of colliding
branes.Comment: 5 pages, 5 figures references adde
Thermal Equilibrium of String Gas in Hagedorn Universe
The thermal equilibrium of string gas is necessary to activate the
Brandenberger-Vafa mechanism, which makes our observed 4-dimensional universe
enlarge. Nevertheless, the thermal equilibrium is not realized in the original
setup, a problem that remains as a critical defect. We study thermal
equilibrium in the Hagedorn universe, and explore possibilities for avoiding
the issue aforementioned flaw. We employ a minimal modification of the original
setup, introducing a dilaton potential. Two types of potential are
investigated: exponential and double-well potentials. For the first type, the
basic evolutions of universe and dilaton are such that both the radius of the
universe and the dilaton asymptotically grow in over a short time, or that the
radius converges to a constant value while the dilaton rolls down toward the
weak coupling limit. For the second type, in addition to the above solutions,
there is another solution in which the dilaton is stabilized at a minimum of
potential and the radius grows in proportion to . Thermal equilibrium is
realized for both cases during the initial phase. These simple setups provide
possible resolutions of the difficulty.Comment: 23 pages,19 figure
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