Large angle MSW solution in grand unified theories withSU(3)×U(1)horizontal symmetry

We construct a model with an $\mathrm{SU}\mathrm{}\left(3\right)\mathrm{}\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ horizontal symmetry in the context of grand unified theories. In our models, the bimaximal lepton mixing and suitable neutrino masses for the large angle MSW solution are obtained without any fine tuning due to the spontaneously broken $\mathrm{SU}(3{)}_{\mathrm{H}}$ symmetry. The three generations of quarks and leptons are unified as members of the $\mathrm{SU}(3{)}_{\mathrm{H}}$ fundamental representation, and the $\mathrm{U}(1{)}_{\mathrm{H}}$ charge gives the origin of the fermion mass hierarchy and mixing angles. We present two explicit examples of $\mathrm{SU}{\mathrm{}\left(5\right)\mathrm{}}_{\mathrm{GUT}}$ and ${\mathrm{SO}\left(10\right)\mathrm{}}_{\mathrm{GUT}}$ models, in which the Yukawa structures are given successfully.