Neutrino Dynamics in Neutron Star Mergers

Neutron star mergers create environments of warm and ultra-dense matter where the strong interaction governs the behavior, but cannot be solved exactly or perturbatively using current methods. These collisions throw matter violently out of equilibrium and provide a unique laboratory to explore the phases and properties of dense matter. Simulations enable us to follow this matter in detail and link it to signals that we can actually observe, such as gravitational waves. Capturing the relevant physics in these simulations is key to reducing uncertainties in what we infer from these signals.

I will focus on the role of neutrinos in merger environments. The local neutrino population influences weak interactions and thereby impacts the equation of state and the gravitational wave signal. I will also present results on a comparison of neutrino distributions from a neutron star merger simulation that uses a Monte Carlo neutrino scheme, which are not necessarily in thermal equilibrium, with Fermi-Dirac (thermally equilibrated) distributions. I will show the impact on the neutrino energy and absorption opacity, as well as the rate of proton fraction change.