Parametric resonance after hilltop inflation caused by an inhomogeneous inflaton field

TL;DR

This paper investigates a novel preheating mechanism after hilltop inflation where inhomogeneous inflaton fields induce parametric resonance in coupled scalar fields, using lattice simulations and analytical methods.

Contribution

It introduces the concept of resonance driven by inhomogeneous inflaton fields post-inflation, expanding understanding of preheating dynamics.

Findings

Resonant enhancement of scalar field fluctuations observed.

Inhomogeneous inflaton fields can trigger parametric resonance.

Resonance amplitudes can surpass initial inflaton fluctuation levels.

Abstract

We study preheating after hilltop inflation where the inflaton couples to another scalar field, e.g. a right-handed sneutrino, which provides a mechanism for generating the correct initial conditions for inflation and also a decay channel for the inflaton that allows for reheating and non-thermal leptogenesis. In the presence of such a coupling, we find that after the phases of tachyonic preheating and tachyonic oscillations, during which the inflaton field becomes inhomogeneous, there can be a subsequent preheating phase where the fluctuations of the other field get resonantly enhanced, from initial vacuum fluctuations up to amplitudes of the same order (and even larger) as the ones of the inflaton field. This resonant enhancement differs from the usual parametric resonance as the inflaton field is inhomogeneous at the time the enhancement takes place. We study this effect using lattice simulations as well as semi-analytically with a generalized Floquet analysis for inhomogeneous background fields.