Chiral gravitational waves from domain walls in Nieh-Yan gravity

TL;DR

This paper investigates how axion domain walls in Nieh-Yan gravity induce parity violation in gravitational waves, resulting in potentially observable circular polarization independent of domain wall tension.

Contribution

It demonstrates that domain walls in Nieh-Yan gravity can produce chiral gravitational waves with polarization unaffected by wall tension, highlighting a novel parity violation mechanism.

Findings

Gravitational waves become circularly polarized after passing through domain walls.

Degree of polarization is independent of domain wall tension.

Domain walls cause parity violation in gravitational wave propagation.

Abstract

We study the scattering of gravitational waves by axion domain walls in teleparallel gravity with the Nieh-Yan term. Since a domain wall causes the parity violation, the transmitted gravitational waves also exhibit the parity violation. We calculate the degree of circular polarization of gravitational waves. It turns out that gravitational waves after going through the domain wall could be chiral. Remarkably, the degree of circular polarization does not depend on the tension of the domain wall.