A note on accelerating cosmologies from compactifications and S-branes

TL;DR

This paper explains recent cosmological solutions with transient acceleration from string theory compactifications and S-branes, highlighting the radion field dynamics and their implications for cosmology.

Contribution

It provides a simple interpretation of accelerating cosmologies from compactifications and S-branes, clarifying their mechanisms and limitations.

Findings

Acceleration occurs at the radion's turning point.

Solutions correspond to radion bouncing off exponential potential.

Interpretation clarifies virtues and limitations of these models.

Abstract

We give a simple interpretation of the recent solutions for cosmologies with a transient accelerating phase obtained from compactification in hyperbolic manifolds, or from S-brane solutions of string/M-theory. In the four-dimensional picture, these solutions correspond to bouncing the radion field off its exponential potential. Acceleration occurs at the turning point, when the radion stops and the potential energy momentarily dominates. The virtues and limitations of these approaches become quite transparent in this interpretation.