On Perturbations in Warm Inflation

TL;DR

This paper explores the dynamics of warm inflation, extending slow-roll parameters, analyzing perturbations, and estimating dissipation, concluding that warm inflation can produce a smooth transition to the radiation era without a preheating phase.

Contribution

It generalizes slow-roll parameters for warm inflation and analyzes entropy and adiabatic perturbations, providing estimates for dissipation and transition to radiation era.

Findings

Entropy perturbations are negligible for small dissipation.

Primordial spectrum is mainly adiabatic.

Universe transitions smoothly to radiation era after inflation.

Abstract

Warm inflation is an interesting possibility of describing the early universe, whose basic feature is the absence, at least in principle, of a preheating or reheating phase. Here we analyze the dynamics of warm inflation generalizing the usual slow-roll parameters that are useful for characterizing the inflationary phase. We study the evolution of entropy and adiabatic perturbations, where the main result is that for a very small amount of dissipation the entropy perturbations can be neglected and the purely adiabatic perturbations will be responsible for the primordial spectrum of inhomogeneities. Taking into account the COBE-DMR data of the cosmic microwave background anisotropy as well as the fact that the interval of inflation for which the scales of astrophysical interest cross outside the Hubble radius is about 50 e-folds before the end of inflation, we could estimate the magnitude of the dissipation term. It was also possible to show that at the end of inflation the universe is hot enough to provide a smooth transition to the radiation era.