Baryon asymmetry, neutrino mixing and supersymmetric SO(10) unification

The baryon asymmetry of the universe can be explained by the out-of-equilibrium decays of heavy right-handed neutrinos. We analyse this mechanism in the framework of a supersymmetric extension of the Standard Model and show that lepton number violating scatterings are indispensable for baryogenesis, even though they may wash-out a generated asymmetry. By assuming a similar pattern of mixings and masses for neutrinos and up-type quarks, as suggested by SO(10) unification, we can generate the observed baryon asymmetry without any fine tuning, if (B - L) is broken at the unification scale Lambda(GUT) similar to 10(16) GeV and, if m(nu mu) similar to 3 x 10(-3) eV as preferred by the MSW solution to the solar neutrino deficit. (C) 1998 Elsevier Science B.V.