Birefringence in fermion-attenuated gravitational wave power spectrum

TL;DR

This paper investigates birefringence effects in the gravitational wave power spectrum within Chern-Simons gravity, highlighting potential observable signatures that could test parity violation and inform early universe physics.

Contribution

It provides a numerical analysis of gravitational wave birefringence in Chern-Simons gravity, predicting distinctive peaks and dips in the power spectrum for future detection.

Findings

Birefringence causes small amplitude differences in gravitational wave polarizations.

Distinctive peaks and dips mirror parametric resonance during reheating.

Predicted observable patterns could be tested by upcoming space-based gravitational wave detectors.

Abstract

Within the framework of Chern-Simons gravity, a theory that dynamically violates parity, we analyze the power spectrum of gravitational waves in light of the damping effect due to the free streaming relativistic neutrinos and dark fermions. The power spectrum is expressed terms of right- and left-handed polarizations, and the evolution of the gravitational waves is studied numerically. Birefringence is explicitly shown in the power spectrum, though the difference in the amplitudes is small. Specific features of peaks and dips appear gravitational wave power spectrum mirroring chiral gravitational wave mediated parametric resonance during reheating. Our result represents a useful tool to test Chern-Simons gravity and enables to constrain mechanisms of inflation and reheating related to this theory. We predict a falsifiable pattern of observable peaks and dips in the chiral independent gravitational power spectrum, eventually observable in next space-borne gravitational interferometers, including LISA, Taiji and Tianqin.