The decays "neutrino{heavy} -> neutrino{light} + photon" and "neutrino{heavy} -> neutrino{light} e+ e-" of massive neutrinos

TL;DR

This paper calculates the decay rates of massive neutrinos into lighter neutrinos with photons or electron-positron pairs, highlighting the dominance of the e+ e- decay mode and estimating their lifetimes.

Contribution

It provides detailed calculations of neutrino decay rates within the standard model, emphasizing the dominance of the e+ e- decay channel over the radiative mode.

Findings

Neutrino decay into lighter neutrino and photon has an extremely long lifetime (~10^44 years).

Decay into lighter neutrino plus e+ e- pair can occur at tree level with a much shorter lifetime (~0.01 year).

The e+ e- decay mode dominates over the photon mode when kinematically allowed.

Abstract

If, as recently reported by the Super-Kamiokande collaboration, the neutrinos are massive, the heaviest one would not be stable and, though chargeless, could in particular decay into a lighter neutrino and a photon by quantum loop effects. The corresponding rate is computed in the standard model with massive Dirac neutrinos as a function of the neutrino masses and mixing angles. The lifetime of the decaying neutrino is estimated to be approximately 10^44 years for a mass 5 10^{-2} eV. If kinematically possible, the decay of a heavy neutrino into a lighter one plus an e+ e- pair occurs at tree level and its one-loop radiative corrections get enhanced by a large logarithm of the electron mass acting as an infrared cutoff. It then largely dominates the photonic mode by several orders of magnitude, corresponding to a lifetime approximately equal to 10^{-2} year for a mass 1.1 MeV.