Anomalous flavor U(1): predictive texture for bi-maximal neutrino mixing

We present a scenario which naturally provides bi-maximal neutrino mixings for a simultaneous explanation of the recent atmospheric and solar neutrino data. A crucial role is played by an anomalous flavor U(1) symmetry, which is also important for a natural understanding of charged fermion mass hierarchies and magnitudes of the CKM matrix elements. Within MSSM the solar neutrino problem can be resolved either through vacuum oscillations or the large mixing angle MSW solution. In supersymmetric GUTs such as SU(5) and SO(10) the MSW solution is realized. If the flavor U(1) also mediates supersymmetry breaking, the vacuum solution in MSSM is eliminated, and only the large mixing angle MSW solution survives.