Minimal Warm Inflation

TL;DR

This paper explores how small couplings of the inflaton to gauge fields can induce thermal effects during inflation, leading to a minimal warm inflation model that alters predictions and fits current data.

Contribution

It introduces a minimal warm inflation model with axion-like couplings that generate a thermal bath, significantly changing inflationary predictions.

Findings

Thermal friction can dominate over Hubble friction during inflation.

The model predicts suppressed tensor-to-scalar ratio and unique non-gaussianities.

Hybrid inflation with axion-like coupling fits current cosmological data.

Abstract

Slow-roll inflation is a successful paradigm. However we find that even a small coupling of the inflaton to other light fields can dramatically alter the dynamics and predictions of inflation. As an example, the inflaton can generically have an axion-like coupling to gauge bosons. Even relatively small couplings will automatically induce a thermal bath during inflation. The thermal friction from this bath can easily be stronger than Hubble friction, significantly altering the usual predictions of any particular inflaton potential. Thermal effects suppress the tensor-to-scalar ratio $r$ significantly, and predict unique non-gaussianities. This axion-like coupling provides a minimal model of warm inflation which avoids the usual problem of thermal backreaction on the inflaton potential. As a specific example, we find that hybrid inflation with this axion-like coupling can easily fit the current cosmological data.