Parametric amplification of metric fluctuations through a bouncing phase

TL;DR

This paper investigates how a cosmological bounce influences scalar metric fluctuations within a simple general relativity framework, revealing potential wave number-dependent effects on the perturbation spectrum relevant for early Universe models.

Contribution

It demonstrates that a bounce can parametrize the amplification of metric fluctuations and affect the scalar perturbation spectrum in a wave number-dependent manner.

Findings

Bounce can amplify metric fluctuations.

Scalar spectrum may depend on wave number after bounce.

Implications for string-inspired early Universe models.

Abstract

We clarify the properties of the behavior of classical cosmological perturbations when the Universe experiences a bounce. This is done in the simplest possible case for which gravity is described by general relativity and the matter content has a single component, namely a scalar field in a closed geometry. We show in particular that the spectrum of scalar perturbations can be affected by the bounce in a way that may depend on the wave number, even in the large scale limit. This may have important implications for string motivated models of the early Universe.