The Dipole of the Astrophysical Gravitational-Wave Background

TL;DR

This paper proposes a method to measure the dipole anisotropy of the astrophysical gravitational-wave background to test the Universe's isotropy, accounting for intrinsic clustering and observer motion effects.

Contribution

It introduces a component separation technique in the gravitational wave context to disentangle kinematic and intrinsic dipoles, enhancing isotropy tests.

Findings

Demonstrates the feasibility of measuring the AGWB dipole with future GW detectors.

Provides a method to separate kinematic and intrinsic dipoles using frequency-dependent observations.

Shows potential for testing the Cosmological Principle with gravitational wave data.

Abstract

One of the main pillars of the {\Lambda}CDM model is the Cosmological Principle, which states that our Universe is statistically isotropic and homogeneous on large scales. Here we test this hypothesis using the Astrophysical Gravitational Wave Background (AGWB) expected to be measured by the Einstein Telescope-Cosmic Explorer network; in particular we perform a numerical computation of the AGWB dipole, evaluating the intrinsic contribution due to clustering and the kinematic effect induced by the observer motion. We apply a component separation technique in the GW context to disentangle the kinematic dipole, the intrinsic dipole and the shot noise (SN), based on the observation of the AGWB at different frequencies. We show how this technique can also be implemented in matched-filtering to minimize the covariance which accounts for both instrumental noise and SN. Since GW detectors are essentially full-sky, we expect that this powerful tool can help in testing the isotropy of our Universe in the next future.