The radion in brane cosmology

Abstract

We consider the homogeneous cosmological radion, which we define as the interbrane distance in a two brane and $Z_2$ symmetrical configuration. In a coordinate system where one of the brane is at rest, the junction conditions for the second (moving) brane give directly the (non-linear) equations of motion for the radion. We analyse the radion fluctuations and solve the non-linear dynamics in some simple cases of interest.

Comments: 24 pages, 4 figures; two figures completed and some comments added in section 7.2; a small section 7.3 added on Randall-Sundrum type of models; some references added