Gravitational-wave signatures of mirror (a)symmetry in binary black hole mergers: measurability and correlation to gravitational-wave recoil

TL;DR

This paper investigates how mirror asymmetries in binary black hole mergers produce circular polarization imbalances in gravitational waves, correlates these with recoil velocities, and assesses measurement prospects with advanced models.

Contribution

It introduces a method to quantify mirror asymmetries in gravitational waves and demonstrates their correlation with black hole recoil, using numerical simulations and surrogate models.

Findings

$V_{GW}$ correlates linearly with black hole recoil helicity.

$V_{GW}$ can be measured accurately at high signal-to-noise ratios.

Surrogate models enable unbiased estimation of $V_{GW}$.

Abstract

Precessing binary black-hole mergers can produce a net flux of circularly-polarized gravitational waves. This imbalance between left- and right-handed circularly polarized waves, quantified via the Stokes pseudo-scalar $V_{\rm GW}$, originated from mirror asymmetries in the binary. We scan the parameter space of black-hole mergers to investigate correlations between $V_{\rm GW}$ and chiral magnitudes constructed out of the intrinsic parameters of the binary. To this end, we use both numerical-relativity simulations for (quasi-circular) and eccentric precessing mergers from both the SXS and RIT catalogues, as well as the state-of-the-art surrogate model for quasi-circular precessing mergers NRSur7dq4. We find that, despite being computed by manifestly different formulas, $V_{\rm GW}$ is linearly correlated to the helicity of the final black hole, defined as the projection of its recoil velocity onto its spin. Next, we test our ability to perform accurate measurements of $V_{\rm GW}$ in gravitational-wave observations through the injection and recovery of numerically simulated signals. We show that $V_{\rm GW}$ can be estimated unbiasedly using the surrogate waveform model NRSur7dq4 even for signal-to-noise ratios of nearly 50, way beyond current gravitational-wave observations.