The 1+1+2 formalism for Scalar-Tensor gravity

We use the 1+1+2 covariant approach to clarify a number of aspects of spherically symmetric solutions of non-minimally coupled scalar tensor theories. Particular attention is focused on the extension of Birkhoff's theorem and the nature of quasi-local horizons in this context.Comment: 27 pages, accepted versio

A new approach to reconstruction methods in f(R)f(R) gravity

We present a new approach of the reconstruction method based on the use of the cosmic parameters instead of a time law for the scale factor. This allows the derivation and analysis of a set of new non-trivial cosmological solutions for $f(R)$-gravity. A number of simple examples are given.Comment: 5 pages, Revtex

Cosmological dynamics of Scalar--Tensor Gravity

We study the phase--space of FLRW models derived from Scalar--Tensor Gravity where the non--minimal coupling is $F(\phi)=\xi\phi^2$ and the effective potential is $V(\phi)=\lambda \phi^n$. Our analysis allows to unfold many feature of the cosmology of this class of theories. For example, the evolution mechanism towards states indistinguishable from GR is recovered and proved to depend critically on the form of the potential $V(\phi)$. Also, transient almost--Friedmann phases evolving towards accelerated expansion and unstable inflationary phases evolving towards stable ones are found. Some of our results are shown to hold also for the String-Dilaton action.Comment: 25 pages, 4 figures, 12 tables, submitted to CQ

Simultaneous expansion and rotation of shear-free universes in modified gravity

We show in a fully covariant way that, there exist a class of $f(R)$ models for which a shear-free, almost FLRW universe can expand and rotate at the same time .Comment: 4 pages, no figures. Contribution submitted to the proceedings of the Spanish Relativity Meeting ERE2011, September 2011, Madrid, Spai