551 research outputs found

### Collapsing sphere on the brane radiates

We study the analogue of the Oppenheimer-Snyder model of a collapsing sphere
of homogeneous dust on the Randall-Sundrum type brane. We show that the
collapsing sphere has the Vaidya radiation envelope which is followed by the
brane analogue of the Schwarzschild solution described by the
Reissner-Nordstrom metric. The collapsing solution is matched to the brane
generalized Vaidya solution and which in turn is matched to the
Reissner-Nordstrom metric. The mediation by the Vaidya radiation zone is the
new feature introduced by the brane. Since the radiating mediation is
essential, we are led to the remarkable conclusion that a collapsing sphere on
the brane does indeed, in contrast to general relativity, radiate null
radiation.Comment: Minor changes, main results remain unchanged, to appear in Phys.
Lett.

### Mass and angular momenta of Kerr anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory

We compute the mass and angular momenta of rotating anti-de Sitter spacetimes
in Einstein-Gauss-Bonnet theory of gravity using a superpotential derived from
standard Noether identities. The calculation relies on the fact that the
Einstein and Einstein-Gauss-Bonnet vacuum equations are the same when
linearized on maximally symmetric backgrounds and uses the recently discovered
D-dimensional Kerr-anti-de Sitter solutions to Einstein's equations

### Kerr-Schild ansatz in Einstein-Gauss-Bonnet gravity: An exact vacuum solution in five dimensions

As is well-known, Kerr-Schild metrics linearize the Einstein tensor. We shall
see here that they also simplify the Gauss-Bonnet tensor, which turns out to be
only quadratic in the arbitrary Kerr-Schild function f when the seed metric is
maximally symmetric. This property allows us to give a simple analytical
expression for its trace, when the seed metric is a five dimensional maximally
symmetric spacetime in spheroidal coordinates with arbitrary parameters a and
b. We also write in a (fairly) simple form the full Einstein-Gauss-Bonnet
tensor (with a cosmological term) when the seed metric is flat and the
oblateness parameters are equal, a=b. Armed with these results we give in a
compact form the solution of the trace of the Einstein-Gauss-Bonnet field
equations with a cosmological term and a different than b. We then examine
whether this solution for the trace does solve the remaining field equations.
We find that it does not in general, unless the Gauss-Bonnet coupling is such
that the field equations have a unique maximally symmetric solution.Comment: 10 pages, no figures, references added. Last version for CQ

### Cosmological perturbations of an expanding brane in an anti-de Sitter bulk: a short review

Since the Randall-Sundrum 1999 papers, braneworlds have been a favourite playground to test string inspired cosmological models. The subject has developped into two main directions : elaborating more complex models in order to strenghten the connection with string theories, and trying to confront them with observations, in particular the Cosmic Microwave Background anisotropies. We review here the latter and see that, even in the simple, "paradigmatic", case of a single expanding brane in a 5D anti-de Sitter bulk, there is still a missing link between the "view from the brane" and the "view from the bulk" which prevents definite predictions

### A note on the Deser-Tekin charges

Perturbed equations for an arbitrary metric theory of gravity in $D$
dimensions are constructed in the vacuum of this theory. The nonlinear part
together with matter fields are a source for the linear part and are treated as
a total energy-momentum tensor. A generalized family of conserved currents
expressed through divergences of anti-symmetrical tensor densities
(superpotentials) linear in perturbations is constructed. The new family
generalizes the Deser and Tekin currents and superpotentials in quadratic
curvature gravity theories generating Killing charges in dS and AdS vacua. As
an example, the mass of the $D$-dimensional Schwarzschild black hole in an
effective AdS spacetime (a solution in the Einstein-Gauss-Bonnet theory) is
examined.Comment: LATEX, 7 pages, no figure

### Kink-antikink, trapping bags and five-dimensional Gauss-Bonnet gravity

Five-dimensional Gauss-Bonnet gravity, with one warped extra-dimension,
allows classes of solutions where two scalar fields combine either in a
kink-antikink system or in a trapping bag configuration. While the
kink-antikink system can be interpreted as a pair of gravitating domain walls
with opposite topological charges, the trapping bag solution consists of a
domain wall supplemented by a non-topological defect. In both classes of
solutions, for large absolute values of the bulk coordinate (i.e. far from the
core of the defects), the geometry is given by five-dimensional anti-de Sitter
space.Comment: 8 pages, 2 figure

### Conserved Charges of Higher D Kerr-AdS Spacetimes

We compute the energy and angular momenta of recent D-dimensional Kerr-AdS
solutions to cosmological Einstein gravity, as well as of the BTZ metric, using
our invariant charge definitions.Comment: 11 pages, references added, equation correcte

### Time-dependent gravitating solitons in five dimensional warped space-times

Time-dependent soliton solutions are explicitly derived in a five-dimensional
theory endowed with one (warped) extra-dimension. Some of the obtained
geometries, everywhere well defined and technically regular, smoothly
interpolate between two five-dimensional anti-de Sitter space-times for fixed
value of the conformal time coordinate. Time dependent solutions containing
both topological and non-topological sectors are also obtained. Supplementary
degrees of freedom can be also included and, in this case, the resulting
multi-soliton solutions may describe time-dependent kink-antikink systems.Comment: 19 pages, 10 figure

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