Neutrino masses and mixing angles in a realistic string-inspired model

We analyze a supersymmetric string-inspired model of all fermion masses and mixing angles based on the Pati-Salam SU(4)×SU(2)_L×SU(2)_R gauge group supplemented by a U(1)_X flavor symmetry. The model involves third family Yukawa unification and predicts the top quark mass and the ratio of the vacuum expectation values tanβ. The model also provides a successful description of the CKM matrix and predicts the masses of the down and strange quarks. However, our main focus is on the neutrino masses and MNS mixing angles, and we show how the recent atmospheric neutrino mixing observed by Super-Kamiokande and the MSW solution to the solar neutrino problem lead to important information about the flavor structure of the model near the string scale. We show how single right-handed neutrino dominance may be implemented by the use of ``Clebsch zeros,'' leading to the LMA MSW solution, corresponding to bimaximal mixing. The LOW MSW and SMA MSW solutions are also discussed.