Sirens Meet Galaxies: Two-Point Statistics of Gravitational Wave Events as a Cosmological Probe

by Michele Mancarella (Centre de Physique Theorique, Marseille)

Monday 19 May 2025, 16:00 → 17:00 Europe/Madrid

Gravitational-wave (GW) sirens are attracting increasing attention in cosmology. While they allow for a direct measurement of the luminosity distance from the GW strain, the source redshift remains inaccessible in the absence of an electromagnetic counterpart. This has led to the development of dark siren techniques, in which redshifts are inferred statistically. A widely used approach involves associating GW events with potential host galaxies from redshift surveys, on an event-by-event basis. However, the growing number of GW detections and the experience of large-scale structure surveys motivate a complementary strategy. In particular, compact binary mergers occur in galaxies and thus trace the same underlying dark matter distribution. This opens the door to cross-correlating GW events with galaxy surveys through two-point statistics. Because GWs and galaxies provide complementary views of the cosmic density field (in luminosity distance and redshift space, respectively), their cross-correlation is a source of cosmological information. After briefly reviewing the foundations and existing implementations of dark siren methodologies, my talk will focus on the use of GW–galaxy cross-correlations as a cosmological probe. Emphasis will be placed on prospects for next-generation ground-based detectors and their synergy with upcoming galaxy surveys, particularly the Euclid mission.