Parity violating gravitational waves at the end of inflation

TL;DR

This paper investigates how parity-violating gravitational waves can be generated at the end of inflation through inflaton-vector interactions, analyzing vector particle production and its impact on gravitational wave spectra.

Contribution

It provides a detailed calculation of vector particle production and its backreaction effects, leading to parity-violating gravitational wave signatures at the end of inflation.

Findings

Vector particles are exponentially produced at the end of inflation.

Parity-violating gravitational waves are sourced by gauge particles.

The gravitational wave spectrum is computed using WKB approximation.

Abstract

Inflaton-vector interactions of the type $\phi F\tilde{F}$ have provided interesting phenomenology to tackle some of current problems in cosmology, namely the vectors could constitute the dark matter component. It could also lead to possible signatures imprinted in a gravitational wave spectrum. Through this coupling, a rolling inflaton induces an exponential production of the transverse polarizations of the vector field, having a maximum at the end of inflation when the inflaton field velocity is at its maximum. These gauge particles, already parity asymmetric, will source the tensor components of the metric perturbations, leading to the production of parity violating gravitational waves. In this work we examine the vector particle production with an attempt to mimic its backreaction effects on the inflation evolution in the weak coupling regime. Furthermore, we fully integrate the gauge particle amplitudes spectrum during this production epoch, studying the behavior until the end of reheating. Finally, we calculate the gravitational wave spectrum solely relying on the vector mode WKB expansion in its regime of validity.