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

TL;DR

This paper proposes a simple D-brane cosmology model where our universe is a boundary D-brane in a 5D anti-de Sitter space, compatible with standard cosmology and potentially testable observationally.

Contribution

It introduces a boundary D-brane cosmology model inspired by Randall--Sundrum scenarios, incorporating a single (3+1)-D brane in a (4+1)-D AdS bulk, aligning with standard cosmology.

Findings

A natural k=+1 closed FLRW universe emerges from the model.

The model can be consistent with standard cosmological observations.

Possible observational tests are suggested.

Abstract

We sketch a particularly simple and compelling version of D-brane cosmology. Inspired by the semi-phenomenological Randall--Sundrum models, and their cosmological generalizations, we develop a variant that contains a single (3+1)-dimensional D-brane which is located on the boundary of a single bulk (4+1)-dimensional region. The D-brane boundary is itself to be interpreted as our visible universe, with ordinary matter (planets, stars, galaxies) being trapped on this D-brane by string theory effects. The (4+1)-dimensional bulk is, in its simplest implementation, adS_{4+1}, anti-de Sitter space. We demonstrate that a k=+1 closed FLRW universe is the most natural option, though the scale factor could quite easily be so large as to make it operationally indistinguishable from a k=0 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.