Brane cosmologies without orbifolds

Abstract

We study the dynamics of branes in configurations where (1) the brane is the edge of a single anti--de Sitter (AdS) space and (2) the brane is the surface of a vacuum bubble expanding into a Schwarzschild or AdS-Schwarzschild bulk. In both cases we find solutions that resemble the standard Robertson-Walker cosmologies, although, in the latter, the evolution can be controlled by a mass parameter in the bulk metric. We also include a term in the brane action for the scalar curvature. This term adds a contribution to the low-energy theory of gravity which does not need to affect the cosmology, but which is necessary for the surface of the vacuum bubble to recover four-dimensional gravity.