Casimir energy and a cosmological bounce

TL;DR

This paper reviews methods for calculating the renormalised energy-momentum tensor of a scalar field in an Einstein Static Universe, exploring implications for energy conditions, inflation, and cosmological bounce scenarios.

Contribution

It compares different computation methods and investigates conditions under which Casimir energy can lead to a cosmological bounce and inflation.

Findings

Equivalence of computation methods for conformally coupled case

Violation of energy conditions for certain couplings and masses

Potential for Casimir energy to source a bounce and inflation

Abstract

We review different computation methods for the renormalised energy momentum tensor of a quantised scalar field in an Einstein Static Universe. For the extensively studied conformally coupled case we check their equivalence; for different couplings we discuss violation of different energy conditions. In particular, there is a family of masses and couplings which violate the weak and strong energy conditions but do not lead to spacelike propagation. Amongst these cases is that of a minimally coupled massless scalar field with no potential. We also point out a particular coupling for which a massless scalar field has vanishing renormalised energy momentum tensor. We discuss the backreaction problem and in particular the possibility that this Casimir energy could both source a short inflationary epoch and avoid the big bang singularity through a bounce.