Non-Gaussian Signatures in the Cosmic Background Radiation from Warm Inflation

TL;DR

The paper investigates non-Gaussian signatures in the Cosmic Microwave Background arising from warm inflation, where radiation production occurs during inflation. It develops a formalism to compute the bispectrum from second-order inflaton perturbations with thermal noise and freeze-out effects, and compares the resulting non-Gaussianity to that of standard, supercooled inflation. For a quartic inflaton potential, the intrinsic warm-inflation bispectrum amplitude A_inf^warm is found to be of the same order as in the standard case, but the dominant contribution comes from second-order gravitational perturbations, giving A_inf ≈ 1 in both models. Consequently, the CMB bispectrum is effectively undetectable with Planck, and any observed large primordial non-Gaussianity would challenge both warm and supercooled single-field inflation.

Abstract

We calculate the bispectrum of the gravitational field fluctuations generated during warm inflation, where dissipation of the vacuum potential during inflation is the mechanism for structure formation. The bispectrum is non--zero because of the self--interaction of the scalar field. We compare the predictions with those of standard, or `supercooled', inflationary models, and consider the detectability of these levels of non--Gaussianity in the bispectrum of the cosmic microwave background. We find that the levels of non--Gaussianity for warm and supercooled inflation are comparable, and over--ridden by the contribution to the bispectrum due to other physical effects. We also conclude that the resulting bispectrum values will be undetectable in the cosmic microwave background for both the MAP and Planck Surveyor satellites.