On the Transfer of Metric Fluctuations when Extra Dimensions Bounce or Stabilize

TL;DR

This paper investigates how metric fluctuations transfer through non-singular bounces or stabilization processes in a universe with an extra compact dimension, using string theory-inspired models.

Contribution

It demonstrates that metric fluctuations pass through bounces and stabilization epochs without disturbance within a string theory-based framework.

Findings

Metric fluctuations transfer undisturbed through bounces.

Radion and metric fluctuations interact in a non-singular background.

Applications to ekpyrotic/cyclic and string gas cosmology are discussed.

Abstract

In this report, we study within the context of general relativity with one extra dimension compactified either on a circle or an orbifold, how radion fluctuations interact with metric fluctuations in the three non-compact directions. The background is non-singular and can either describe an extra dimension on its way to stabilization, or immediately before and after a series of non-singular bounces. We find that the metric fluctuations transfer undisturbed through the bounces or through the transients of the pre-stabilization epoch. Our background is obtained by considering the effects of a gas of massless string modes in the context of a consistent 'massless background' (or low energy effective theory) limit of string theory. We discuss applications to various approaches to early universe cosmology, including the ekpyrotic/cyclic universe scenario and string gas cosmology.