Radiative decay and magnetic moment of neutrinos in matter

Abstract

Effects of a medium on the radiative decay and the magnetic moments of neutrinos are studied in a simple Feynman-diagram approach. It is shown that even though the radiative decay rate is dramatically increased in a medium, the magnetic moments, both diagonal and off diagonal, are not enhanced in the medium from their vacuum value due to the coherence condition of the medium effects. It is also shown that there cannot be any helicity flip in a medium due to the weak interactions alone, independently from the interaction with a magnetic field.