Propagation of Gravitational Waves in Chern-Simons Axion Einstein Gravity

TL;DR

This paper studies how gravitational waves propagate in a string-inspired modified gravity theory with axion and Chern-Simons coupling, revealing polarization-dependent dispersion relations and comparing with standard $F(R)$ gravity.

Contribution

It investigates gravitational wave propagation in a string-motivated axion Einstein gravity with Chern-Simons coupling, highlighting polarization asymmetries and differences from $F(R)$ gravity.

Findings

Dispersion relations differ for right- and left-handed polarization modes.

Polarization states exhibit distinct propagation characteristics.

Comparison shows deviations from standard $F(R)$ gravity.

Abstract

In this paper we shall investigate the propagation of gravitational waves in a flat Friedman-Robertson-Walker background, in the context of a string motivated corrected Einstein gravity. Particularly, we shall consider a misalignment axion Einstein gravity in the presence of a string originating Chern-Simons coupling of the axion field to the Chern-Pontryagin density in four dimensions. We shall focus our study on the propagation of the gravitational waves, and we shall investigate whether there exists any difference in the propagation of the polarization states of the gravitational waves. As we demonstrate, the dispersion relations are different in the Right-handed mode and the Left-handed mode. Finally, we compare the propagation of the axion Chern-Simons Einstein theory with that of standard $F(R)$ gravity.