A New Probe of Gravitational Parity Violation Through (Non-)Observation of the Stochastic Gravitational-Wave Background

TL;DR

This paper explores how the stochastic gravitational-wave background can be used to detect or constrain gravitational parity violation, providing new bounds and forecasting future improvements with advanced detectors.

Contribution

It introduces a novel method to probe gravitational parity violation using the stochastic gravitational-wave background, including current constraints and future forecasts with upgraded detectors.

Findings

Current non-detection constrains birefringent parameters to ~0.1

Future third-generation detectors could improve constraints by over two orders of magnitude

The study provides a new powerful probe of gravitational parity violation

Abstract

Parity violation in the gravitational sector is a prediction of many theories beyond general relativity. In the propagation of gravitational waves, parity violation manifests by inducing amplitude and/or velocity birefringence between right- and left-circularly polarized modes. We study how the stochastic gravitational wave background can be used to place constraints on these birefringent effects. We consider two model scenarios, one in which we allow birefringent corrections to become arbitrarily large, and a second in which we impose stringent theory priors. In the former, we place constraints on a generic birefringent gravitational-wave signal due to the current non-detection of a stochastic background from compact binary events. We find a joint constraint on birefringent parameters, $\kappa_D$ and $\kappa_z$, of $\mathcal{O}(10^{-1})$. In the latter scenario, we forecast constraints on parity violating theories resulting from observations of the future upgraded LIGO-Virgo-KAGRA network as well as proposed third-generation detectors. We find that third-generation detectors will be able to improve the constraints by at least two orders of magnitude, yielding new stringent bounds on parity violating theories. This work introduces a novel and powerful probe of gravitational parity violation with gravitational-wave data.