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}\sim 10^{16} $GeV and, if $m_{\n_\m} \sim 3\cdot 10^{-3} $eV as preferred by the MSW solution to the solar neutrino deficit.