Large angle MSW solution in grand unified theories with SU(3)XU(1) horizontal symmetry - art. no. 016008

We construct a model with an SU(3) X U(1) horizontal symmetry in the contex t of grand unified theories. In our models, the bimaximal lepton mixing and suitable neutrino masses for the large angle MSW solution are obtained wit hout any fine tuning due to the spontaneously broken SU(3)(H) symmetry. The three generations of quarks and leptons are unified as members of the SU(3 )(H) fundamental representation, and the U(1)(H) charge gives the origin of the fermion mass hierarchy and mixing angles. We present two explicit exam ples of SU(5) GUT and SO(10)(GUT) models, in which the Yukawa structures ar e given successfully.