3,413 research outputs found
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.
On boundary terms and conformal transformations in curved space-times
We intend to clarify the interplay between boundary terms and conformal
transformations in scalar-tensor theories of gravity. We first consider the
action for pure gravity in five dimensions and show that, on compactifing a la
Kaluza-Klein to four dimensions, one obtains the correct boundary terms in the
Jordan (or String) Frame form of the Brans-Dicke action. Further, we analyze
how the boundary terms change under the conformal transformations which lead to
the Pauli (or Einstein) frame and to the non-minimally coupled massless scalar
field. In particular, we study the behaviour of the total energy in
asymptotically flat space-times as it results from surface terms in the
Hamiltonian formalism.Comment: LaTeX 2e, 12 pages, no figure
Classical dynamics and stability of collapsing thick shells of matter
We study the collapse towards the gravitational radius of a macroscopic
spherical thick shell surrounding an inner massive core. This overall
electrically neutral macroshell is composed by many nested delta-like massive
microshells which can bear non-zero electric charge, and a possibly non-zero
cosmological constant is also included. The dynamics of the shells is described
by means of Israel's (Lanczos) junction conditions for singular hypersurfaces
and, adopting a Hartree (mean field) approach, an effective Hamiltonian for the
motion of each microshell is derived which allows to check the stability of the
matter composing the macroshell. We end by briefly commenting on the quantum
effects which may arise from the extension of our classical treatment to the
semiclassical level.Comment: 16 pages in IOP style, 8 figures, accepted for publication in Class.
Quantum Gra
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