Quantum nature of cosmological bounces

TL;DR

This paper investigates the quantum characteristics of cosmological bounces, especially focusing on how quantum effects influence the bounce's behavior and the surrounding space-time using new effective equations for interacting matter.

Contribution

It introduces new effective equations for quantum cosmology with interacting matter, highlighting the role of squeezed states and their impact on the bounce and space-time.

Findings

Bounce proven for uncorrelated states

Squeezed states significantly influence the bounce

New effective equations differ from free scalar models

Abstract

Several examples are known where quantum gravity effects resolve the classical big bang singularity by a bounce. The most detailed analysis has probably occurred for loop quantum cosmology of isotropic models sourced by a free, massless scalar. Once a bounce has been realized under fairly general conditions, the central questions are how strongly quantum it behaves, what influence quantum effects can have on its appearance, and what quantum space-time beyond the bounce may look like. This, then, has to be taken into account for effective equations which describe the evolution properly and can be used for further phenomenological investigations. Here, we provide the first analysis with interacting matter with new effective equations valid for weak self-interactions or small masses. They differ from the free scalar equations by crucial terms and have an important influence on the bounce and the space-time around it. Especially the role of squeezed states, which have often been overlooked in this context, is highlighted. The presence of a bounce is proven for uncorrelated states, but as squeezing is a dynamical property and may change in time, further work is required for a general conclusion.