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

Non-minimally coupled scalar fields in homogeneous universes

The equations governing the evolution of non-minimally coupled scalar matter and the scale factor of a Robertson-Walker universe are derived from a minisuperspace action. As for the minimally coupled case, it is shown that the entire semiclassical dynamics can be retrieved from the Wheeler-DeWitt equation via the Born-Oppenheimer reduction, which properly yields the (time-time component of the) covariantly conserved energy-momentum tensor of the scalar field as the source term for gravity. However, for a generic coupling, the expectation value of the operator which evolves the matter state in time is not equal to the source term in the semiclassical Einstein equation for the scale factor of the universe and the difference between these two quantities is related to the squeezing and quantum fluctuations of the matter state. We also argue that matter quantum fluctuations become relevant in an intermediate regime between quantum gravity and semiclassical gravity and study several cases in detail.Comment: REVTeX, 24 pages, 12 EPS figures included. Accepted for publication in Phys. Rev.

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