Blue Tensor Spectrum from Particle Production during Inflation

TL;DR

This paper proposes a particle production mechanism during inflation that generates a detectable, chiral, and non-gaussian blue gravitational wave spectrum, compatible with current observational constraints and testable with polarization data.

Contribution

It introduces a novel mechanism involving vector quanta from a pseudo-scalar field that produces a distinctive GW spectrum during inflation, avoiding scalar perturbation overproduction.

Findings

Produces a detectable, chiral, non-gaussian GW spectrum

Compatible with BICEP2 and Planck constraints

Potential to reconstruct the pseudo-scalar potential from GW data

Abstract

We discuss a mechanism of particle production during inflation that can result in a blue gravitational wave (GW) spectrum, compatible with the BICEP2 result and with the r < 0.11 limit on the tensor-to-scalar ratio at the Planck pivot scale. The mechanism is based on the production of vector quanta from a rolling pseudo-scalar field. Both the vector and the pseudo-scalar are only gravitationally coupled to the inflaton, to keep the production of inflaton quanta at an unobservable level (the overproduction of non-gaussian scalar perturbations is a generic difficulty for mechanisms that aim to generate a visible GW signal from particle production during inflation). This mechanism can produce a detectable amount of GWs for any inflationary energy scale. The produced GWs are chiral and non-gaussian; both these aspects can be tested with large-scale polarization data (starting from Planck). We study how to reconstruct the pseudo-scalar potential from the GW spectrum.