Density Fluctuations in Thermal Inflation and Non-Gaussianity

TL;DR

This paper explores how thermal inflation affects primordial fluctuations, proposing a mechanism to generate curvature perturbations at the end of thermal inflation that can produce significant non-Gaussianity, thus impacting model viability.

Contribution

It introduces a novel mechanism for generating primordial curvature perturbations at the end of thermal inflation using a fluctuating coupling, allowing certain inflation models to remain consistent with observations.

Findings

Thermal inflation shifts horizon-exit to later times, affecting the power spectrum.

The proposed mechanism can produce large non-Gaussianity.

Some inflation models can be compatible with observations despite thermal inflation.

Abstract

We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 $e$-folds after the standard inflation, the time of horizon-exit during inflation corresponding to the present observational scale shifts toward the end of inflation. It generally makes the primordial power spectrum more deviated from a scale-invariant one and hence renders some models inconsistent with observations. We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We show that, by adopting the mechanism, some inflation models can be liberated even in the presence of the thermal inflation. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario.