Exploring the string axiverse and parity violation in gravity with gravitational waves

TL;DR

This paper investigates how axion fields and Chern-Simons gravity coupling could produce observable signatures in gravitational waves, and uses current data to set stringent limits on these effects, significantly improving previous bounds.

Contribution

It provides the first constraints on Chern-Simons coupling and axion abundance from gravitational wave observations, enhancing previous bounds by several orders of magnitude.

Findings

No signatures of parametric resonance or polarization were observed in gravitational wave data.

The Chern-Simons coupling constant is constrained to be less than 10^{8} km, much tighter than previous limits.

The results improve our understanding of axion physics and parity violation in gravity.

Abstract

We show that the parametric resonance of gravitational waves occurs due to the axion coherent oscillation and the circular polarization of gravitational waves is induced by the Chern-Simons coupling. However, we have never observed these signatures in the data of gravitational waves. Using this fact, we give stringent constraints on the Chern-Simons coupling constant $\ell$ and the abundance of the light string axion. In particular, we improved the current bound $\ell\leq10^{8}\,\,{\rm km}$ by many orders of magnitude.