4,359 research outputs found
On the gravitational collapse in anti-de Sitter space-time
We study the semiclassical evolution of a self-gravitating thick shell in
Anti-de Sitter space-time. We treat the matter on the shell as made of
quantized bosons and evaluate the back-reaction of the loss of gravitational
energy which is radiated away as a non-adiabatic effect. A peculiar feature of
anti-de Sitter is that such an emission also occurs for large shell radius,
contrary to the asymptotically flat case.Comment: Changed to Elsevier style, 9 pages, 1 figure. Minor typos corrected.
Accepted for publication in Phys. Lett.
Gauss-Bonnet Brane Cosmology with Radion Stabilization
We study cosmology in a five-dimensional brane-world with a stabilizing
effective potential for the radion and matter localized on the two branes. We
consider the corrections induced by the Gauss-Bonnet contribution to the total
action performing and expansion around the two possible static solutions up to
second order in the ratio between brane matter energy density and brane
tensions. The Friedmann and acceleration equations on the visible brane are
obtained and discussed.Comment: To be published in Phys.Rev.D, References Adde
Thermodynamics of a collapsing shell in an expanding Universe
We describe the quasi-static collapse of a radiating, spherical shell of
matter in de Sitter space-time using a thermodynamical formalism. It is found
that the specific heat at constant area and other thermodynamical quantities
exhibit singularities related to phase transitions during the collapse.Comment: 9 pages, 2 figures, accepted for publication in Phys. Lett.
Charged False Vacuum Bubbles and the AdS/CFT Correspondence
We initiate a study of cosmology within the framework of Maldacena's AdS/CFT
correspondence. We present a comprehensive analysis of the classical motion of
a charged domain wall that separates an external Reissner-Nordstrom region of
spacetime (with small or vanishing cosmological constant) from an internal
de-Sitter region. The possible associated spacetime diagrams are drawn,
although in the classical case, an unambiguous prediction of what occurs at
late times in the interior region is not possible, since singularities and
Cauchy horizons form. We argue that, when the asymptotic region is anti-de
Sitter, the AdS/CFT correspondence gives a prescription for resolving the
curvature singularities and evolving solutions across the expected Cauchy
horizon. Some of our solutions contain inflating interiors, and we provide
evidence these can be patched onto solutions with smooth initial data,
circumventing an obstacle found by Farhi and Guth to creating an inflating
universe in the laboratory.Comment: 21 pages, 6 figures, latex, references and some comments adde
Quantized shells as a tool for studying semiclassical effects in general relativity
Thin shells in general relativity can be used both as models of collapsing
objects and as probes in the space-time outside compact sources. Therefore they
provide a useful tool for the analysis of the final fate of collapsing matter
and of the effects induced in the matter by strong gravitational fields. We
describe the radiating shell as a (second quantized) many-body system with one
collective degree of freedom, the (average) radius, by means of an effective
action which also entails a thermodynamic description. Then we study some of
the quantum effects that occur in the matter when the shell evolves from an
(essentially classical) large initial radius towards the singularity and
compute the corresponding backreaction on its trajectory.Comment: 4 pages, uses espcrc2.sty, no figures, talk given at the Third
meeting on constrained dynamics and quantum gravity (QG99), Sardinia, Sept
199
Second order brane cosmology with radion stabilization
We study cosmology in the five-dimensional Randall-Sundrum brane-world with a
stabilizing effective potential for the radion and matter localized on the
branes. The analysis is performed by employing a perturbative expansion in the
ratio rho/V between the matter energy density on the branes and the brane
tensions around the static Randall-Sundrum solution (which has rho=0 and brane
tensions +-V). This approach ensures that the matter evolves adiabatically and
allows us to find approximate solutions to second order in \rho/V. Some
particular cases are then analyzed in details.Comment: 17 pages, RevTeX4, 4 figures, final version to appear in Phys. Rev.
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