Scalar perturbations in regular two-component bouncing cosmologies

TL;DR

This paper analyzes scalar perturbations in a two-component bouncing cosmology, revealing that the pre-bounce growing mode does not transfer to the post-bounce dominant mode, which may instead become isocurvature dominated.

Contribution

It demonstrates that the pre-bounce growing mode of the Bardeen potential is not transferred to the post-bounce dominant mode in two-component regular cosmologies.

Findings

Pre-bounce growing mode not transferred to post-bounce dominant mode

Post-bounce mode may be dominated by isocurvature component

Results challenge previous claims in the literature

Abstract

We consider a two-component regular cosmology bouncing from contraction to expansion, where, in order to include both scalar fields and perfect fluids as particular cases, the dominant component is allowed to have an intrinsic isocurvature mode. We show that the spectrum of the growing mode of the Bardeen potential in the pre-bounce is never transferred to the dominant mode of the post-bounce. The latter acquires at most a dominant isocurvature component, depending on the relative properties of the two fluids. Our results imply that several claims in the literature need substantial revision.