Lepton Production by Neutrinos in AN External Electromagnetic Field

We study two processes of lepton production by high-energy neutrinos in an external electromagnetic field: (i) the decay of a massive neutrino into an electron-positron pair and a light neutrino in the framework of the theory with neutrino mixing; (ii) the annihilation of a muon neutrino and an electron antineutrino into a muon and a positron. The asymptotic behavior of the lepton production rates as the functions of the kinematic and field parameters are investigated. We discuss the possibility of observing of the external field effects and some astrophysical applications.