Graceful exit from inflation and reheating with twin waterfalls

TL;DR

This paper explores a hybrid inflation model with pseudo-Nambu-Goldstone boson inflaton and waterfall fields, demonstrating a mechanism for reheating and dark matter production via waterfall dynamics and symmetries.

Contribution

It introduces a novel hybrid inflation framework with specific symmetries that ensure flatness, facilitate reheating, and naturally produce dark matter candidates.

Findings

Reheating temperature is sufficiently high due to Higgs portal couplings.

The model naturally includes a dark matter candidate from waterfall fields.

Preheating can produce the correct relic density of waterfall dark matter.

Abstract

We study the hybrid inflation with a pseudo-Nambu-Goldstone boson inflaton and two waterfall scalar fields. The $Z_2$ symmetry for the waterfall fields keeps inflaton potential flat against quantum corrections coming from the waterfall couplings, and it is broken spontaneously in the vacuum without a domain wall problem within the Hubble horizon of our universe. We show that the $Z_2$ invariant Higgs portal couplings to the waterfall fields are responsible for the reheating process, leading to a sufficiently large reheating temperature after inflation. In the presence of an extra $Z'_2$ symmetry, one of the waterfall fields or another singlet scalar field becomes a dark matter candidate. In particular, we find that preheating is sufficient to account for the correct relic density of the waterfall dark matter.