Neutrino Quantum Kinetics in Neutron Star Mergers

Neutrinos play a pivotal role in neutron star mergers. They drive outflows from the remnant accretion disk and change the ratios of protons and neutrons that later combine to form heavy elements, possibly shaping the origin of the lion's share of r-process heavy elements in the universe. These processes are very sensitive to how many of each flavor of neutrino pass through the ejected matter, but a proper treatment of both radiation transport and the quantum mechanical flavor-changing phenomena is a highly challenging problem. There has nevertheless been immense progress in recent years. I will describe a tiered approach to developing reliable models of neutrino processes in mergers, including sub-grid modeling, approximate and exact mean-field quantum kinetics simulations, and attempts at justifying mean-field models with many-body calculations. I will further present novel large-scale, multidimensional simulations of neutrino quantum kinetics in realistic merger environments. This work aims to bridge neutrino phenomenology with other uncertain physics in extreme conditions, moving toward a comprehensive understanding of dynamics and element formation in these extraordinary events.