Cosmological perturbations from inhomogeneous preheating and multi-field trapping

TL;DR

This paper explores a novel multi-field trapping model where inhomogeneous preheating generates curvature perturbations during a weak inflationary phase, differing from traditional trapped inflation scenarios by not requiring an unstable ESP.

Contribution

It introduces a new mechanism for curvature perturbation generation via inhomogeneous preheating in multi-field trapping without relying on unstable ESP points.

Findings

Curvature perturbations can be generated during shoulder inflation induced by trapping.

The mechanism differs from traditional trapped inflation by not assuming an unstable ESP.

Inhomogeneous preheating at late times can enhance curvature fluctuations for low-scale inflation.

Abstract

We consider inhomogeneous preheating in a multi-field trapping model. The curvature perturbation is generated by inhomogeneous preheating which induces multi-field trapping at the enhanced symmetric point (ESP), and results in fluctuation in the number of e-foldings. Instead of considering simple reheating after preheating, we consider a scenario of shoulder inflation induced by the trapping. The fluctuation in the number of e-foldings is generated during this weak inflationary period, when the additional light scalar field is trapped at the local maximum of its potential. The situation may look similar to locked or thermal inflation or even to hybrid inflation, but we will show that the present mechanism of generating the curvature perturbation is very different from these others. Unlike the conventional trapped inflationary scenario, we do not make the assumption that an ESP appears at some unstable point on the inflaton potential. This assumption is crucial in the original scenario, but it is not important in the multi-field model. We also discuss inhomogeneous preheating at late-time oscillation, in which the magnitude of the curvature fluctuation can be enhanced to accommodate low inflationary scale.