Baryon asymmetry and neutrino mixing

In theories where B - L is a spontaneously broken local symmetry, the cosmological baryon asymmetry can be generated by the out-of-equilibrium decay of heavy Majorana neutrinos. We study this mechanism assuming a similar pattern of mixing and masses for leptons and quarks, as suggested by SO(10) unification. This implies that B - L is broken at the unification scale ΛGUT ∼ 1016 GeV, if mνμ ∼ 3 · 10−3eV as preferred by the MSW explanation of the solar neutrino deficit. The observed value of the baryon asymmetry, nBs ∼ 10−10, is then obtained without any fine tuning of parameters.