Gravitational reheating in Starobinsky inflation

TL;DR

This paper explores whether gravitational interactions alone can reheat the universe after Starobinsky inflation, finding that both perturbative and non-perturbative processes can produce sufficiently high temperatures without additional fields.

Contribution

It demonstrates that gravitational particle production can account for reheating in Starobinsky inflation without assuming extra inflaton couplings.

Findings

Reheating temperature of ~10^8 GeV with minimal coupling.

Non-perturbative effects can reach temperatures of ~10^12 GeV.

Reheating duration is approximately 21 e-folds.

Abstract

We investigate the possibility of achieving post-inflationary reheating exclusively through the gravitational interaction in Starobinsky inflation, which itself assumes nothing but gravity. We consider the possibility that the reheating sector couples to gravity via a non-minimal coupling. Our analysis is performed both in a perturbative and in a non-perturbative approach, where particle production is computed from Bogoliubov coefficients. Our findings indicate that, for a minimal coupling, a reheating temperature $T_\text{reh}\sim 10^{8}$~GeV is obtained, with a reheating duration of approximately 21 $e$-folds. We also show that non perturbative gravitational production during preheating can lead to maximum temperatures of the order of $10^{12}$ GeV. This shows that the gravitational interaction could be the sole responsible for reheating the Universe after inflation, without the need to assume other \emph{ad hoc} inflaton interactions.