Matter creation in a nonsingular bouncing cosmology

TL;DR

This paper investigates reheating mechanisms in a nonsingular bouncing cosmology, finding Parker particle production alone can reheat the universe effectively without additional interactions.

Contribution

It demonstrates that Parker particle production during the bounce is sufficient for reheating, reducing the need for interaction-based particle creation in this cosmological model.

Findings

Parker particle production can reheat the universe to high temperatures.

Interaction-based particle creation requires large coupling to significantly contribute.

The Ekpyrotic phase helps eliminate anisotropies while leaving the universe cold post-bounce.

Abstract

We examine reheating in the two-field matter bounce cosmology. In this model, the universe evolves from a matter-dominated phase of contraction to an Ekpyrotic phase of contraction before the nonsingular bounce. The Ekpyrotic phase frees the model from unwanted anisotropies, but leaves the universe cold and empty of particles after the bounce. For this reason, we explore two particle production mechanisms which take place during the course of the cosmological evolution: Parker particle production where the matter field couples only to gravity and particle creation via interactions between the matter field and the bounce field. Although we show that both mechanisms can produce particles in this model, we find that Parker particle production is sufficient to reheat the universe to high temperatures. Thus there is {\it{a priori}} no need to add an interaction term to the Lagrangian of the model. Still, particle creation via interactions can contribute to the formation of matter and radiation, but only if the coupling between the fields is tuned to be large.