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 demonstrate the necessity to take into account lepton number violating scatterings which can wash-out an asymmetry and are nevertheless indispensable for baryogenesis. 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 $\Lambda_{GUT}\sim 10^{16}$ GeV and, if $m_{\nu_\mu}\sim 3 10^{-3}$ eV as preferred by the MSW solution to the solar neutrino deficit.