MASSIVE NEUTRINOS AND THE WEAK SCALE SINGLET MAJORON

We consider the phenomenology of the singlet majoron model of Chikashige, Mohapatra and Peccei in the case where lepton number is broken at the weak scale. This scenario naturally leads to a see-saw mechanism for the neutrino masses in which the light neutrinos are close to their experimental limits. A fourth generation can also be incorporated in a natural way. We argue that this model is compatible with all experimental, astrophysical, and cosmological constraints at present, but can be stringently tested by experiments in the near future. First, we show that the rates for flavor-changing neutrino decays into majorons in this model can evade cosmological limits. Second, we consider the "triviality" bounds for the case in which the symmetry is broken by light scalars, and show that these are much more stringent for this model than for the standard model. Third, we consider majoron production through couplings to the electroweak symmetry breaking sector, both for the case in which the symmetries are broken by light scalars and for a non-linear realization of the broken symmetry. For the scalar case, we find that much of the parameter space of the model can be probed by collider and rare decay experiments in the near future. For the non-linear case, we find that the cross section for majoron production is probably too small to be observed at the SSC, even under rather optimistic theoretical assumptions. However, in this case, we argue that the scale of new physics is well below SSC energies, so that there would be a good chance of seeing new physics at the SSC.