The importance of being warm (during inflation)

TL;DR

This paper explores how warm inflation, sustained by dissipative particle production at high temperatures, modifies inflationary predictions, making some models compatible with observational data that are otherwise ruled out.

Contribution

It demonstrates that warm inflation alters the scalar spectrum and tensor-to-scalar ratio, expanding the range of models consistent with Planck observations.

Findings

Warm inflation lowers the tensor-to-scalar ratio.

Quartic chaotic potential aligns with Planck data in warm inflation.

Warm inflation models can be compatible with observations unlike vacuum models.

Abstract

The amplitude of primordial curvature perturbations is enhanced when a radiation bath at a temperature T>H is sustained during inflation by dissipative particle production, which is particularly significant when a non-trivial statistical ensemble of inflaton fluctuations is also maintained. Since gravitational modes are oblivious to dissipative dynamics, this generically lowers the tensor-to-scalar ratio and yields a modified consistency relation for warm inflation, as well as changing the tilt of the scalar spectrum. We show that this alters the landscape of observationally allowed inflationary models, with for example the quartic chaotic potential being in very good agreement with the Planck results for nearly-thermal inflaton fluctuations, whilst essentially ruled out for an underlying vacuum state. We also discuss other simple models that are in agreement with the Planck data within a renormalizable model of warm inflation.