Neutrino spin-flavor oscillations derived from the mass basis

We reconsider the standard scheme for description of neutrino spin-flavor oscillations aiming at a rigorous derivation of evolution equation for the mixed flavor neutrino states in magnetic field. For this purpose we obtain the evolution equation in the physical basis of massive neutrinos and then trace its transformation into the flavor basis. The effective Hamiltonian of the resulting equation relevant to interaction with the magnetic field differs from the standard one by several entries. The approach leads to interesting relations of the neutrino magnetic moments defined in the two neutrino bases and to some additional subtle properties of the formalism.