Cosmology in Horava-Witten M-Theory

TL;DR

This paper investigates how Horava-Witten M-Theory can produce standard cosmology, finding that static solutions only work with pure radiation, but time-dependent moduli may allow realistic cosmological evolution.

Contribution

It demonstrates conditions under which Horava-Witten M-Theory can yield standard Friedmann-Robertson-Walker cosmology, highlighting the role of dynamic moduli and brane matter.

Findings

Static solutions require pure radiation on branes.

Time-dependent moduli can enable standard cosmology.

Inconsistencies arise with fixed moduli and static solutions.

Abstract

The cosmology of the Horava-Witten M-Theory reduced to five dimensions retaining the volume modulus is considered. Brane matter is considered as a perturbation on the vacuum solution, and the question of under what circumstances does the theory give rise to the standard RWF cosmology is examined. It is found that for static solutions, one obtains a consistent solution of the bulk field equations and the brane boundary conditions only for pure radiation on the branes. (A similar result holds if additional 5-branes are added in the bulk.) If one stabilizes the fifth dimension in an ad hoc manner, a similar inconsistency still occurs (at least for a Hubble constant that has no dependence on y, the fifth dimension.) Within this framework, the possibility of recovering the RWF cosmology still remains if the volume modulus and /or the distance between branes becomes time dependent, under which circumstances the Hubble constant must then depend on y (unless the fifth dimension and volume modulus expand at precisely the same rate).