Massive Neutrino Decays

Neutrino physics is used as an illustrative example for an elementary introduction to the computational method of Feynman loop-diagrams and decay rates. If the neutrinos are as massive as recently reported by the Super-Kamiokande results, the heaviest neutrino $\nu_H$ would not be stable. Although chargeless, it could decay -- by quantum loop effect -- into a lighter neutrino $ \nu_L$ by emitting a photon: $\nu_H \to \nu_L + \gamma $. If kinematically possible, the $\nu_H \to \nu_L$ + e$^+$ + e$^-$ mode could occur at the tree diagram level and furthermore get enhanced, at one-loop radiative corrections, by a large logarithm of the electron mass acting as an infrared cutoff.