The Ups and Downs of Cyclic Universes

TL;DR

This paper explores oscillating cosmological models with multiple fluids and energy transfer, revealing new behaviors but suggesting they are unlikely solutions to the flatness problem.

Contribution

It provides exact solutions for cyclic universes with energy exchange, expanding understanding of non-equilibrium effects in cosmology.

Findings

New exact solutions for cyclic cosmologies

Energy transfer impacts expansion behavior

Unlikely to solve the flatness problem

Abstract

We investigate homogeneous and isotropic oscillating cosmologies with multiple fluid components. Transfer of energy between these fluids is included in order to model the effects of non-equilibrium behavior on closed universes. We find exact solutions which display a range of new behaviors for the expansion scale factor. Detailed examples are studied for the exchange of energy from dust or scalar field into radiation. We show that, contrary to expectation, it is unlikely that such models can offer a physically viable solution to the flatness problem.