Hill crossing during preheating after hilltop inflation

TL;DR

This paper investigates the nonlinear dynamics during preheating after hilltop inflation, revealing that inflaton fluctuations can lead to regions crossing the potential maximum, forming oscillon-like structures instead of stable domain walls.

Contribution

It demonstrates through lattice simulations that inflaton fluctuations can cause hilltop crossing and oscillon formation during preheating, a novel insight into post-inflation dynamics.

Findings

Inflaton fluctuations grow enough to cause hill crossing.

Formation of oscillon-like structures during preheating.

Hill crossing regions are not stable domain walls.

Abstract

In 'hilltop inflation', inflation takes place when the inflaton field slowly rolls from close to a maximum of its potential (i.e. the 'hilltop') towards its minimum. When the inflaton potential is associated with a phase transition, possible topological defects produced during this phase transition, such as domain walls, are efficiently diluted during inflation. It is typically assumed that they also do not reform after inflation, i.e. that the inflaton field stays on its side of the 'hill', finally performing damped oscillations around the minimum of the potential. In this paper we study the linear and the non-linear phases of preheating after hilltop inflation. We find that the fluctuations of the inflaton field during the tachyonic oscillation phase grow strong enough to allow the inflaton field to form regions in position space where it crosses 'over the top of the hill' towards the 'wrong vacuum'. We investigate the formation and behaviour of these overshooting regions using lattice simulations: Rather than durable domain walls, these regions form oscillon-like structures (i.e. localized bubbles that oscillate between the two vacua) which should be included in a careful study of preheating in hilltop inflation.