Brane cosmologies without orbifolds - art. no. 105009

We study the dynamics of branes in configurations where (1) the brane is th e edge of a single anti-de Sitter (AdS) space and (2) the brane is the surf ace 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 controll ed by a mass parameter in the bulk metric. We also include a term in the br ane action for the scalar curvature. This term adds a contribution to the l ow-energy theory of gravity which does not need to affect the cosmology, bu t which is necessary for the surface of the vacuum bubble to recover four-d imensional gravity.