Leptogenesis in left–right symmetric theories

The masses and mixing of the light left-handed neutrinos can be related to those of the heavy right-handed neutrinos in left–right symmetric theories. Properties of the light neutrinos are measured in terrestrial experiments and the CP-violating decays of their heavy counterparts produce a baryon asymmetry via the well-known leptogenesis mechanism. The left-handed Higgs triplet, present in left–right symmetric theories, modifies the usual see-saw formula. It is possible to relate the lepton asymmetry to the light neutrino parameters when the triplet and the top quark through the usual see-saw mechanism give the dominant contribution to the neutrino mass matrix. We find that in this situation the small angle MSW and vacuum solutions produce reasonable asymmetry, whereas the large angle MSW case requires extreme fine-tuning of the three phases in the mixing matrix.