Shrinking the Warm Little Inflaton

TL;DR

This paper demonstrates that warm inflation can be achieved with a single fermionic field whose mass oscillates with the inflaton, suppressing large oscillations and parametric resonance effects, simplifying the model.

Contribution

It introduces a minimal warm inflation model with oscillatory fermion mass, removing the need for additional symmetries or multiple fermions.

Findings

Warm inflation is viable with a single oscillating fermion.

Oscillatory mass suppresses large eta parameter oscillations.

Parametric resonance effects are negligible on CMB scales.

Abstract

We show that warm inflation can be successfully realized in the high temperature regime through dissipative interactions between the inflaton and a single fermionic degree of freedom, provided that the latter's mass is an oscillatory function of the inflaton field value. We demonstrate, in particular, that despite the consequent large amplitude oscillations of the eta slow-roll parameter, their effect is, on average, sufficiently suppressed to allow for a slow-roll trajectory. In addition, we demonstrate that, even though this also induces a parametric resonance that amplifies inflaton perturbations, this has a negligible effect on CMB scales in the relevant parametric range. Hence, the "Warm Little Inflaton" scenario can be realized with one less fermionic degree of freedom and no need of imposing an additional discrete interchange symmetry.