Neutrino Quantum Kinetics

TL;DR

This paper derives quantum kinetic equations for neutrino flavor evolution in dense, hot environments, incorporating effects of coherence, collisions, and spin dynamics, relevant for astrophysical phenomena like supernovae.

Contribution

It provides a fundamental derivation of QKEs from quantum field theory, including new spin evolution equations and their potential impact on neutrino-antineutrino conversion.

Findings

QKEs describe coherent flavor evolution with effective mass.

Collision terms reduce to Boltzmann equations under certain conditions.

Spin equations enable possible neutrino-antineutrino transformation.

Abstract

We present a formulation of the quantum kinetic equations (QKEs) which govern the evolution of neutrino flavor at high density and temperature. Here, the QKEs are derived from the ground up, using fundamental neutrino interactions and quantum field theory. We show that the resulting QKEs describe coherent flavor evolution with an effective mass when inelastic scattering is negligible. The QKEs also contain a collision term. This term can reduce to the collision term in the Boltzmann equation when scattering is dominant and the neutrino effective masses and density matrices become diagonal in the interaction basis. We also find that the QKE's include equations of motion for a new dynamical quantity related to neutrino spin. This quantity decouples from the equations of motion for the density matrices at low densities or in isotropic conditions. However, the spin equations of motion allow for the possibility of coherent transformation between neutrinos and antineutrinos at high densities and in the presence of anisotropy. Although the requisite conditions for this exist in the core collapse supernova and compact object merger environments, it is likely that only a self consistent incorporation of the QKEs in a sufficiently realistic model could establish whether or not significant neutrino-antineutrino conversion occurs.