Bi-maximal neutrino mixing and anomalous flavor U(1)

We describe how bi-maximal neutrino mixing can be realized in realistic models based on MSSM and SUSY GUTS such as SU(5) and SO (10). A crucial role is played by an anomalous U(1) flavor symmetry, which also helps understand the observed charged fermion mass hierarchies and the magnitudes of the CKM matrix elements. While in MSSM a variety of solutions for the solar neutrino puzzle are possible, SUSY SU(5) and SO(10) only permit the large mixing angle MSW solution. Models in which the U(1) symmetry also mediates SUSY breaking allow both tile large mixing angle and tile low MSW solutions. We also present renormalization group studies for the neutrino mass matrix, generated through the U(1) flavor symmetry. Our analysis shows that renormalization does not change the desirable picture of bi-maximal mixing.