Neutrino spin kinetics in a medium with magnetic field

The neutrino spin kinetic equation in a medium with a magnetic field is derived, with the inclusion of the self-consistent electromagnetic field in a plasma. In order to check the proposed approach we reproduce the known results for the Dirac neutrino helicity change in constant and twisting magnetic fields. The new neutrino helicity change channel affected by the linear-polarized Alfven wave of a finite amplitude propagating along the general magnetic field ${\mathbf{B}}_0$ is considered. In contrast with the known cases, this channel arises for the longitudinal neutrino propagation p∥${\mathbf{B}}_0$, where p is the neutrino momentum.