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 noncompact directions. The background is nonsingular and can either describe an extra dimension on its way to stabilization, or immediately before and after a series of nonsingular bounces. We find that the metric fluctuations transfer undisturbed through the bounces or through the transients of the 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.

• Received 10 October 2005

DOI:https://doi.org/10.1103/PhysRevD.73.086002