Cosmological Expansion in the Presence of an Extra Dimension

TL;DR

This paper addresses the inconsistency in brane-world cosmology by incorporating cosmological constants, enabling realistic expansion rates during nucleosynthesis and faster early universe expansion, with implications for baryogenesis.

Contribution

It demonstrates that adding cosmological constants to the brane and bulk resolves the problematic Friedmann equation in brane-world models.

Findings

Normal expansion during nucleosynthesis is achievable.

Faster-than-normal early universe expansion is possible.

Potential implications for electroweak baryogenesis.

Abstract

It has recently been pointed out that global solutions of Einstein's equations for a 3-brane universe embedded in 4 spatial dimensions give rise to a Friedmann equation of the form H ~ rho on the brane, instead of the usual H ~ (rho)^{1/2}, which is inconsistent with cosmological observations. We remedy this problem by adding cosmological constants to the brane and the bulk, as in the recent scenario of Randall and Sundrum. Our observation allows for normal expansion during nucleosynthesis, but faster than normal expansion in the very early universe, which could be helpful for electroweak baryogenesis, for example.