  If the neutrino is Majorana type and the electroweak phase transition is
second or weak first order, neutrino-induced interactions together with
sphaleron transitions have the potential to erase a previously generated baryon
asymmetry of the universe. Taking correctly into account the evolution of the
vacuum expectation of the Higgs field the effective light neutrino masses are
constrained to be lighter than order 10 MeV, while the effective heavy masses
are constrained to be heavier than order 10^7 GeV.
