Model-independent search for anisotropies in stochastic gravitational-wave backgrounds and application to LIGO-Virgo’s first three observing runs

A stochastic gravitational-wave (GW) background consists of a large number weak, independent and uncorrelated events astrophysical or cosmological origin. The GW power on the sky is assumed to contain anisotropies top an isotropic component, i.e., angular monopole. Complementary LIGO--Virgo--KAGRA (LVK) searches, we develop efficient analysis pipeline compute maximum-likelihood anisotropic maps in backgrounds directly pixel domain using data folded over one sidereal day. We invert full pixel-pixel correlation matrix map-making sky, up optimal eigenmode cutoff decided systematically simulations. In addition modeled mapping, implement model-independent method probe spectral shapes backgrounds. Using from LIGO--Virgo's first three observing runs, obtain upper limits as well monopole limiting case, consistent with LVK results. also set constraints shape this novel method.