Bounds on neutrino masses from neutrino decay rates, cosmology and the see-saw mechanism

We study the constraints imposed on the masses of νe, νμ and νT on the basis of direct experimental bounds, cosmological bounds, theoretical calculations of neutrino decay rates, experimental bounds on related decay charged leptons and the structure of neutrino mass matrices in the “see-saw” mechanism. We consider standard model amplitudes as well as contributions from all “beyonds standard” models. Assuming a simple “reasonable” form of the see-saw mechanism, we derive the bounds: m(νT) ⩽ 65 eV, m(νggm) ⩽ 4 eV, m(νe) ⩽ 0.02eV, M(WR) ⩾ 50 PeV. Possible ways of evading these boundsare discussed.