M/String Theory, S-branes and Accelerating Universe

TL;DR

This paper explores how hyperbolic compactification of M/string theory with S-branes can lead to a transient acceleration of the universe, potentially explaining late-time cosmic acceleration and addressing the coincidence problem.

Contribution

It analyzes the cosmological implications of S-brane related compactifications, proposing a model that aligns with observational data and offers a solution to the coincidence problem.

Findings

Transient acceleration compatible with observations

KK modes have wavelengths comparable to observable universe

Proposes a link between dark energy density and universe's dimensionality

Abstract

Recently it was observed that the hyperbolic compactification of M/string theory related to S-branes may lead to a transient period of acceleration of the universe. We study time evolution of the corresponding effective 4d cosmological model supplemented by cold dark matter and show that it is marginally possible to describe observational data for the late-time cosmic acceleration in this model. However, investigation of the compactification 11d -> 4d suggests that the Compton wavelengths of the KK modes in this model are of the same order as the size of the observable part of the universe. Assuming that this problem, as well as several other problems of this scenario, can be resolved, we propose a possible solution of the cosmological coincidence problem due to relation between the dark energy density and the effective dimensionality of the universe.