  Majorana masses of the neutrino implies lepton number violation and is
intimately related to the lepton asymmetry of the universe, which gets related
to the baryon asymmetry of the universe in the presence of the sphalerons
during the electroweak phase transition. Assuming that the baryon asymmetry of
the universe is generated before the electroweak phase transition, it is
possible to dicriminate different classes of models of neutrino masses. While
see-saw mechanism and the triplet higgs mechanism are preferred, the Zee-type
radiative models and the R-parity breaking models requires additional inputs to
generate baryon asymmetry of the universe during the electroweak phase
transition.
