Realization of the large mixing angle solar neutrino solution in an SO (10) supersymmetric grand unified model - art. no. 073010

An SO(10) supersymmetric grand unified model proposed earlier leading to th e solar solution involving "just-so" vacuum oscillations is reexamined to s tudy its ability to obtain the other possible solar solutions. It is found that all four viable solar neutrino oscillation solutions can be achieved i n the model simply by modification of the right-handed Majorana neutrino ma ss matrix M-R. Whereas the small mixing and vacuum solutions are easily obt ained with several texture zeros in M-R, the currently favored large mixing angle solution requires a nearly geometric hierarchical form for M-R that leads by the seesaw formula to a light neutrino mass matrix which has two o r three texture zeros. The form of the matrix which provides the "fine-tuni ng" necessary to achieve the large mixing angle solution can be understood in terms of Froggatt-Nielsen diagrams for the Dirac and right-handed Majora na neutrino mass matrices. The solution satisfies several leptogenesis requ irements which in turn can be responsible for the baryon asymmetry in the u niverse.