Revisiting a pre-inflationary radiation era and its effect on the CMB power spectrum

TL;DR

This paper investigates how a pre-inflationary radiation era with a thermal inflaton distribution affects the CMB power spectrum, providing constraints on inflation duration and inflaton temperature using WMAP and Planck data.

Contribution

It introduces a detailed analysis of a pre-inflationary radiation era with thermal inflaton, deriving a divergence-free power spectrum and constraining inflation parameters with observational data.

Findings

Power spectrum free from infrared divergences.

Best-fit inflation duration less than 1 e-fold beyond solving cosmological problems.

Only an upper bound on inflaton temperature obtained.

Abstract

We revisit the scenario where inflation is preceded by a radiation era by considering that the inflaton too could have been in thermal equilibrium early in the radiation era. Hence we take into account not only the effect of a pre-inflationary era on the inflaton mode functions but also that of a frozen thermal distribution of inflaton quanta. We initially discuss in detail the issues relevant to our scenario of a pre-inflationary radiation dominated era and then obtain the scalar power spectrum for this scenario. We find that the power spectrum is free from infrared divergences. We then use the WMAP and Planck data to determine the constraints on the inflaton comoving `temperature' and on the duration of inflation. We find that the best fit value of the duration of inflation is less than 1 e-folding more than what is required to solve cosmological problems, while only an upper bound on the inflaton temperature can be obtained.