Beyond Isotropic Gravitational Waves: Search for Anisotropies with Pulsar Timing Arrays

Recent analyses by pulsar timing arrays (PTAs) have provided evidence for the detection of a stochastic gravitational wave background (SGWB). Standard analyses assume an isotropic, unpolarized background, yielding the Hellings–Downs angular correlation between pulsar pairs. Departures from this expectation, through anisotropy or polarization, could reveal new physics. In this work, our goal is to develop a generalized estimator for the Overlap Reduction Function (ORF) based on [1], with an aim to apply it to the PTA data to test the standard assumptions of SGWB.

[1] Kumar & Kamionkowski, Phys. Rev. Lett. 133, 151401 (2024)