SUPERSYMMETRIC SO(10) FOR FERMION MASSES AND MIXINGS: RANK-1 STRUCTURES OF FLAVOR

We consider a supersymmetric SO(10) model with a SU(3) symmetry of flavour in which fermion masses emerge via the see-saw mixing with superheavy fermions in 16+16bar representations. In this model the dangerous D=5 operators of proton decay are naturally suppressed and flavour-changing supersymmetric effects are under control. The mass matrices for all fermion types (up and down quarks, charged leptons as well as neutrinos) appear in the form of combinations of three rank-1 matrices, common to all types of fermions, with different coefficients that are successive powers of small parameters, related to each other by SO(10) symmetry properties. Two versions of the model are considered, in which approximate grand unification of masses takes place between quarks and leptons of the first family (with very small tan β) or for the ones of the second family (predicting moderate tan β ≃ 7–8). The second version exhibits an interesting mechanism of unification of the determinants of the Yukawa matrices of all types of fermions at the GUT scale and it provides a perfect fit of the known data for fermion masses, mixing and CP-violation. It predicts a hierarchical pattern of neutrino masses with non-zero θe3 , within 2-7 degrees. In addition, it predicts the correct sign of the baryon asymmetry of the Universe via the leptogenesys scenario.