Democratic mass matrices from broken O(3)(L) x O(3)(R) flavor symmetry

We impose O(3)(L) X O(3)(R) flavor symmetry in the supersymmetric standard model. Three lepton doublets l(i) transform as an O(3)(L) triplet and three charged leptons (e) over bar(i) as an O(3)(R) triplet, while Higgs doubler s H and (H) over bar are O(3)(L) X O(3)(R) singlets. We discuss a flavor O( 3)(L) X O(3)(R) breaking mechanism that leads to "successful" phenomenologi cal mass matrices, so-called "democratic" ones, in which the large nu(mu)-n u(tau) mixing is naturally obtained. Three neutrinos have nearly degenerate masses of order 0.1 eV which may be accesible to future double beta-decay experiments, We extend our approach to the quark sector and show that it is well consistent with the observed quark mass hierarchies and the CKM matri x elements. However, the large mass of the top quark requires a relatively large coupling constant. (C) 1999 Published by Elsevier Science B.V. All ri ghts reserved.