Applying Cosmological Principle to Better Probe the Redshift Evolution of Binary Black Hole Merger Rate

Gravitational waves inform about the probable distances at which an observed signal originated. This information when combined over multiple observations is used in the modeling of the redshift evolution of the merger rate. This is an important aspect of binary black hole population analysis which is expected to have close ties with the star formation history of the universe or dynamical evolution of star clusters. At the least, it can probe the time delay between the star formation and merger of remnants. However, due to the degeneracy between the inclination angle of the binary and the luminosity distance, the measured luminosity distance has large uncertainty that limits our ability to precisely measure the redshift distribution of mergers. In this letter, we show that by imposing the cosmological principle it is possible to suppress this uncertainty and better discriminate between different distributions modeling the redshift evolution of binary black hole merger rate. Additionally, we show that by making a comparison with an analysis that does not make such imposition we can probe the cosmological principle.