Gravity waves and non-Gaussian features from particle production in a sector gravitationally coupled to the inflaton

TL;DR

This paper investigates how particle production during inflation can generate observable gravitational waves and non-Gaussian features, especially through models involving a pseudoscalar field, while maintaining consistency with observational constraints.

Contribution

It introduces models of particle production in a gravitationally coupled sector that can produce detectable gravitational waves and non-Gaussianities without disrupting standard inflation predictions.

Findings

Localized features in scalar spectrum and bispectrum may be observable.

Gravitational wave signatures are generally suppressed without additional effects.

Relativistic gauge field production can produce observable B-mode polarization.

Abstract

We study the possibility that particle production during inflation could source observable gravity waves on scales relevant for Cosmic Microwave Background experiments. A crucial constraint on such scenarios arises because particle production can also source inflaton perturbations, and might ruin the usual predictions for a nearly scale invariant spectrum of nearly Gaussian curvature fluctuations. To minimize this effect, we consider two models of particle production in a sector that is only gravitationally coupled to the inflaton. For a single instantaneous burst of massive particle production, we find that localized features in the scalar spectrum and bispectrum might be observable, but gravitational wave signatures are unlikely to be detectable (due to the suppressed quadrupole moment of non-relativistic quanta) without invoking some additional effects. We also consider a model with a rolling pseudoscalar that leads to a continuous production of relativistic gauge field fluctuations during inflation. Here we find that gravitational waves from particle production can actually exceed the usual inflationary vacuum fluctuations in a regime where non-Gaussianity is consistent with observational limits. In this model observable B-mode polarization can be obtained for any choice of inflaton potential, and the amplitude of the signal is not necessarily correlated with the scale of inflation.