Heating up the cold bounce

TL;DR

This paper explores bouncing cosmological models where a smooth transition from contraction to expansion occurs, leading to a cold universe that is subsequently heated by amplified gauge fields, resulting in a perturbative gauge coupling.

Contribution

It demonstrates how gauge field amplification during a bounce can reheat the universe and stabilize the gauge coupling at a perturbative level.

Findings

The universe remains cold immediately after the bounce.

Amplified gauge fields reheat the universe effectively.

Gauge coupling stabilizes at a constant, perturbative value.

Abstract

Self-dual string cosmological models provide an effective example of bouncing solutions where a phase of accelerated contraction smoothly evolves into an epoch of decelerated Friedmann--Robertson--Walker expansion dominated by the dilaton. While the transition to the expanding regime occurs at sub-Planckian curvature scales, the Universe emerging after the bounce is cold, with sharply growing gauge coupling. However, since massless gauge bosons (as well as other massless fields) are super-adiabatically amplified, the energy density of the maximally amplified modes re-entering the horizon after the bounce can efficiently heat the Universe. As a consequence the gauge coupling reaches a constant value, which can still be perturbative.