UC San Diego

The subject of this dissertation is the evolution of neutrino distributions in hot, dense astrophysical environments, such as the early Universe, core collapse supernovae or compact object mergers. This is an important problem in astrophysics because the dynamics and the composition of these systems can be strongly influenced by neutrinos, leading to potential modification of nucleosynthesis and of astrophysical observables. In these environments, neutrinos can undergo both coherent forward scattering and direction-changing or inelastic collisions. The transport equations for flavored neutrinos, or quantum kinetic equations (QKEs), are derived from first principles, beginning with quantum field theory and Standard Model neutrino interactions. The QKEs can reduce to the standard Schrödinger-like equations for neutrino flavor evolution in the limit of low matter density, and to a Boltzmann-like equation describing neutrino scattering at high density. In addition, in high-density, anisotropic environments we find a novel process that can mediate coherent exchange of particle number and flavor information between neutrino and antineutrino states (spin coherence). We discuss the prospects for modification of the standard picture of neutrino flavor evolution in supernovae and other astrophysical environments by non- forward scattering and spin coherence