First astrometric constraints on parity-violation in the gravitational wave background

TL;DR

This paper presents the first astrometric constraints on parity-violating stochastic gravitational wave background signals using quasar proper motion data from Gaia DR3 and VLBA, establishing a new observational approach.

Contribution

It introduces a novel method to probe parity violation in the gravitational wave background through astrometric measurements, complementing existing pulsar timing techniques.

Findings

Constraints on parity-violating SGWB amplitude: -0.020 ± 0.025 (Gaia DR3)

Constraints on parity-violating SGWB amplitude: -0.004 ± 0.010 (VLBA)

Frequency range of analysis: 4.2×10⁻¹⁸ Hz to 1.1×10⁻⁸ Hz

Abstract

Astrometry, the precise measurement of stellar positions and velocities, offers a promising approach to probing the low-frequency stochastic gravitational wave background (SGWB). Notably, astrometric vector sky maps are sensitive to parity-violating SGWB signals, which cannot be distinguished using pulsar timing array observations in an isotropic SGWB. We present the first astrometric constraints on parity-violating SGWB using quasar catalogs from Gaia DR3 and VLBA data. By analyzing the $EB$ correlation in the two-point correlation function of the proper motions of the quasars, we find 2$\sigma$ constraints on the parity-violating SGWB amplitude $h_{70}^2\Omega_{V} = -0.020 \pm 0.025$ from Gaia DR3 and $h_{70}^2\Omega_{V} = -0.004 \pm 0.010$ from VLBA. These constraints are valid in the frequency range $4.2 \times 10^{-18}\,{\rm Hz} < f < 1.1 \times 10^{-8}\,{\rm Hz}$. Although not currently a tight constraint on theoretical models, this first attempt lays the groundwork for future investigations using more precise astrometric data.