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 2σ constraints on the parity-violating SGWB amplitude h702ΩV=−0.020±0.025 from Gaia DR3 and h702ΩV=−0.004±0.010 from VLBA. These constraints are valid in the frequency range 4.2×10−18Hz<f<1.1×10−8Hz. Although not currently a tight constraint on theoretical models, this first attempt lays the groundwork for future investigations using more precise astrometric data.
@article{arxiv.2505.18085,
title = {First astrometric constraints on parity-violation in the gravitational wave background},
author = {Santiago Jaraba and Sachiko Kuroyanagi and Qiuyue Liang and Meng-Xiang Lin and Mark Trodden},
journal= {arXiv preprint arXiv:2505.18085},
year = {2026}
}