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 ντ on the basis of direct experimental bounds, cosmological bounds, theoretical calculations of neutrino decay rates, experimental bounds on related decays of 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 'beyond standard' models. Assuming a simple 'reasonable' form of the see-saw mechanism, we derive the bounds: m(ντ) ≤ 65 eV, m(νμ) ≤ 4 eV, m(νe) ≤ 0.02 eV, M(WR) ≥ 50 PeV. Possible ways of evading these bounds are discussed. (orig.)