Living on the edge: cosmology on the boundary of anti-de Sitter space

Abstract

We sketch a particularly simple and compelling version of D-brane cosmology. Inspired by the semi-phenomenological Z. Randall--Sundrum models, and their cosmological generalizations, we develop a variant that contains a single 3q1- Z. dimensional D-brane which is located on the boundary of a single bulk 4q1-dimensional region. The D-brane boundary is Z. itself to be interpreted as our visible universe, with ordinary matter planets, stars, galaxies being trapped on this D-brane by Z. string theory effects. The 4q1-dimensional bulk is, in its simplest implementation, adS , anti-de Sitter space. We 4q1 demonstrate that a ksq1 closed FLRW universe is the most natural option, though the scale factor could quite easily be so Z large as to make it operationally indistinguishable from a ks0 spatially flat universe. With minor loss of elegance, . spatially flat and hyperbolic FLRW cosmologies can also be accommodated. We demonstrate how this model can be made consistent with standard cosmology, and suggest some possible observational tests. q 2000 Elsevier Science B.V. All rights reserved