Incorporating neutron star physics into gravitational wave inference with neural priors

Bayesian inference, widely used in gravitational-wave parameter estimation, depends on the choice of priors, i.e., on our previously existing knowledge. However, to investigate neutron star mergers, priors are often chosen in an agnostic way, leaving valuable information from nuclear physics and independent observations of neutron stars unused. In this work, we propose to encode information on neutron star physics into data-driven prior distributions constructed with normalizing flows, referred to as neural priors. These priors take input from constraints on the nuclear equation of state and neutron star population models. Applied to GW170817, GW190425, and GW230529, we highlight two contributions of the framework. First, we demonstrate its ability to provide source classification and to enable model selection of equation of state constraints for loud signals such as GW170817, directly from the gravitational-wave data. Second, we obtain narrower constraints on the source properties through these informed priors. As a result, the neural priors consistently recover higher luminosity distances compared to agnostic priors. Our method paves the way for classifying future ambiguous low-mass mergers observed through gravitational waves and for continuously incorporating advances in our understanding of neutron star properties into gravitational-wave data analysis.