Note on the Radion Effective Potential in the Presence of Branes

In String Theory compactification, branes are often invoked to get the desired form of the radion effective potential. Current popular way of doing this assumes that the introduction of branes will not modify the background geometry in an important way. In this paper, we show by an explicit example that at least in the codimension 2 case, the gravitational backreaction of the brane cannot be neglected in deriving the radion effective potential. Actually, in this case, the presence of branes will have no effect on the dynamics of radion.Comment: 6 pages, no figures. Some discussion clarified, conclusion unchanged. To appear in Phys. Rev.

Gravitational potential in Palatini formulation of modified gravity

General Relativity has so far passed almost all the ground-based and solar-system experiments. Any reasonable extended gravity models should consistently reduce to it at least in the weak field approximation. In this work we derive the gravitational potential for the Palatini formulation of the modified gravity of the L(R) type which admits a de Sitter vacuum solution. We conclude that the Newtonian limit is always obtained in those class of models and the deviations from General Relativity is very small for a slowly moving source.Comment: 5 pages, no figure