Quantum field theory treatment of neutrino spin-flavor oscillations in a magnetic field

We study spin-flavor oscillations of neutrinos in a magnetic field within the quantum field theory approach in which neutrinos are virtual particles. Neutrinos are taken to be Majorana particles having a nonzero transition magnetic moment. We derive the dressed propagators of the neutrino mass eigenstates exactly accounting for the magnetic field contribution. The matrix element and the transition probability for spin-flavor oscillations are obtained. The leading term in the transition probability is shown to coincide with the result of the standard quantum mechanical description of neutrino oscillations. We also derive the correction to the transition probability which has the quantum field theory origin.