Neutrino spin evolution in presence of general external fields

The derivation of the quasiclassical Lorentz invariant neutrino spin evolution equation taking into account general types of neutrino non-derivative interactions with external fields is presented. We discuss the constraints on the characteristics of matter and neutrino under which this quasiclassical approach is valid. The application of the obtained equation for the case of the Standard Model neutrino interactions with moving and polarized background matter is considered.