Scalar induced gravitational waves from Chern-Simons gravity during inflation era

TL;DR

This paper studies how Chern-Simons gravity during inflation affects scalar-induced gravitational waves, revealing that parity violation introduces polarization but with negligible effects on large scales.

Contribution

It provides a semi-analytic method to evaluate the polarization of SIGWs in Chern-Simons gravity during inflation, highlighting the minimal impact of parity violation on large scales.

Findings

Parity violation induces polarization in SIGWs.

The correction from the CS term is negligible on large scales.

Degree of circular polarization remains very small.

Abstract

We investigate the scalar induced gravitational waves (SIGWs) in the Chern-Simons (CS) gravity with a dynamical scalar field during slow roll inflation. Due to the parity violation in the CS term, the SIGWs are generally polarized, which are effectively characterized by the degree of circular polarization. We derive the semianalytic expression to evaluate the power spectra and the degree of circular polarization of the SIGWs, which receive contributions from the general relativity and the parity-violating term, respectively. We find that the correction from the parity-violating CS term is negligible on large scales, which means that the degree of circular polarization of SIGWs is very small.