Chiral gravitational waves from domain walls in Nieh-Yan gravity

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.