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

We impose O(3)L×O(3)R flavor symmetry in the supersymmetric standard model. Three lepton doublets ℓi transform as an O(3)L triplet and three charged leptons ei as an O(3)R triplet, while Higgs doublets H and H are O(3)L×O(3)R singlets. We discuss a flavor O(3)L×O(3)R breaking mechanism that leads to “successful” phenomenological mass matrices, so-called “democratic” ones, in which the large νμ–ντ mixing is naturally obtained. Three neutrinos have nearly degenerate masses of order 0.1 eV which may be accesible to future double β-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 matrix elements. However, the large mass of the top quark requires a relatively large coupling constant.