Testing the nature of gravitational wave propagation using dark sirens and galaxy catalogues

The dark sirens method enables us to use gravitational wave events without electromagnetic counterparts as tools for cosmology and tests of gravity. Furthermore, the dark sirens analysis code GWCOSMO can now robustly account for information coming from both galaxy catalogues and the compact object mass distribution. We present here an extension of the GWCOSMO code and methodology to constrain parameterized deviations from General Relativity that affect the propagation of gravitational waves under the Lambda CDM expansion history of the universe. We show results of our analysis using data from the GWTC3 gravitational wave catalogues, in preparation for application to the O4 observing run. After testing our pipelines using the First Two Years mock data set, we reanalyse 46 events from GWTC-3, and combine the posterior for BBH and NSBH sampling results for the first time. We obtain joint constraints on H0 and parameterized deviations from General Relativity in the Power Law + Peak BBH population model. With increased galaxy catalogue support in the future, our work sets the stage for dark sirens to become a powerful tool for testing gravity.