B-L violating nucleon decay and GUT scale baryogenesis in SO(10)

We show that grand unified theories based on SO(10) generate naturally the next-to-leading baryon number violating operators of dimension seven. These operators, which violate (B - L), lead to unconventional decays of the nucleon such as n -> e(-) K+, e(-) pi(+) and p -> nu pi(+). In two-step breaking schemes of nonsupersymmetric SO(10), nucleon lifetime for decays into these modes is found to be within reach of experiments. We also identify supersymmetric scenarios where these decays may be accessible, consistent with gauge coupling unification. Further, we show that the (B - L) asymmetry generated in the decays of GUT scale scalar bosons and/or gauge bosons can explain consistently the observed baryon asymmetry of the universe. The induced (B - L) asymmetry is sphaleron-proof, and survives down to the weak scale without being erased by the electroweak interactions. This mechanism works efficiently in a large class of nonsupersymmetric and supersymmetric SO(10) models, with either a 126(H) or a 16(H) Higgs field employed for rank reduction. In minimal models the induced baryon asymmetry is tightly connected to the masses of quarks, leptons and neutrinos and is found to be compatible with observations.