Vector fluctuations from multidimensional curvature bounces

TL;DR

This paper investigates the behavior of vector fluctuations during multidimensional curvature bounces, showing that in five-dimensional models, vector modes can be significantly amplified and remain continuous across the bounce, unlike simpler models.

Contribution

It provides a detailed analysis of vector mode evolution in multidimensional bouncing cosmologies, highlighting conditions for amplification and continuity across the bounce.

Findings

Vector fluctuations are continuous across smooth curvature bounces.

In five-dimensional models, vector modes can be strongly amplified.

Multidimensional models exhibit richer vector mode dynamics than simpler cases.

Abstract

It is argued that in the case of a smooth transition across a (dilaton-driven) curvature bounce the growing mode of the vector fluctuations matches continuously with a decaying mode at later times. Analytical examples of this observation are given both in the presence and in the absence of fluid sources. In the case of multidimensional bouncing models the situation is different, since the system of differential equations describing the vector modes of the geometry has a richer structure. The amplification of the vector modes of the geometry is specifically investigated in a regular five-dimensional bouncing curvature model where scale factors of the external and internal manifolds evolve at a dual rate. Vector fluctuations, in this case, can be copiously produced and are continuous across the bounce. The relevance of these results is critically illustrated.