Exotic see-saw mechanism for neutrinos and leptogenesis in a Pati-Salam model

We discuss non-perturbative corrections to the neutrino sector, in the context of a d-brane pati-salam-like model, that can be obtained as a simple alternative to so(10) gut’s in theories with open and unoriented strings. in such d-brane models, exotic stringy instantons can correct the right-handed neutrino mass matrix in a calculable way, thus affecting mass hierarchies and modifying the see-saw mechanism to what we name exotic see-saw. for a wide range of parameters, a compact spectrum of right-handed neutrino masses can occur that gives rise to a predictive scenario for low energy observables. this model also provides a viable mechanism for baryon asymmetry in the universe (bau) through leptogenesis. finally, a majorana mass for the neutron is naturally predicted in the model, leading to potentially testable neutron-antineutron oscillations. combined measurements in neutrino and neutron-antineutron sectors could provide precious informations on physics at the quantum gravity scale.