Viable inflationary models ending with a first-order phase transition

TL;DR

This paper analyzes hybrid inflation models ending with a first-order phase transition, exploring their parameter space to find models consistent with observations, despite challenges from bubble nucleation and spectral index constraints.

Contribution

It provides an exact analysis of hybrid inflation regimes ending with bubble production and assesses the viability of these models against current observational data.

Findings

Viable models exist with bubble production compatible with observations.

The analysis covers the full parameter space of Linde's second-order hybrid model.

Models can produce nearly scale-invariant density perturbations despite constraints.

Abstract

We investigate the parameter space of hybrid inflation models where inflation terminates via a first-order phase transition causing nucleation of bubbles. Such models experience a tension from the need to ensure nearly scale invariant density perturbations, while avoiding a near scale-invariant bubble size distribution which would conflict observations. We perform an exact analysis of the different regimes of the models, where the energy density of the inflaton field ranges from being negligible as compared to the vacuum energy to providing most of the energy for inflation. Despite recent microwave anisotropy results favouring a spectral index less than one, we find that there are still viable models that end with bubble production and can match all available observations. As a by-product of our analysis, we also provide an up-to-date assessment of the viable parameter space of Linde's original second-order hybrid model across its full parameter range.