Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

TL;DR

This paper explores how a pseudoscalar inflaton can generate parity-violating signals in the CMB through gauge field interactions, predicting observable TB and EB correlations in future experiments.

Contribution

It provides a detailed calculation of parity-violating tensor modes from a pseudoscalar inflaton and discusses scenarios where these effects could be detected in upcoming CMB observations.

Findings

Parity-violating tensor modes can produce detectable TB and EB correlations.

The model predicts specific amplitudes consistent with current data.

Future experiments may observe these parity-violating signals.

Abstract

If the inflaton is a pseudoscalar, then it naturally interacts with gauge fields via an axion-like coupling to $F_{\mu\nu} \tilde{F}^{\mu\nu}$. Through this coupling, the rolling inflaton produces quanta of the gauge field, that in their turn source the tensor components of the metric perturbations. Due to the parity-violating nature of the system, the right- and the left-handed tensor modes have different amplitudes. Such an asymmetry manifests itself in the form of non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB). We compute the amplitude of the parity-violating tensor modes and we discuss two scenarios, consistent with the current data, where parity-violating CMB correlation functions will be detectable in future experiments.