Broken S3 flavor symmetry of leptons and quarks: Mass spectra and flavor mixing patterns

We apply the discrete S-3 flavor symmetry to both lepton and quark sectors of the Standard Model extended by introducing one Higgs triplet and realizing the type-II seesaw mechanism for finite neutrino masses. The resultant mass matrices of charged leptons (M-l), neutrinos (M-v), up-type quarks (M-u) and down-type quarks (M-d) have a universal form consisting of two terms: one is proportional to the identity matrix 1 and the other is proportional to the democracy matrix D. We argue that the textures of M-l, M-u and Md are dominated by the D term, while that of M is dominated by the I term. This hypothesis implies a near mass degeneracy of three neutrinos and can naturally explain why the mass matrices of charged fermions are strongly hierarchical, why the quark mixing matrix is close to I and why the lepton mixing matrix contains two large angles. We discuss a rather simple perturbation ansatz to break the S-3 symmetry and obtain more realistic mass spectra of leptons and quarks as well as their flavor mixing patterns. We stress that the I term, which used to be ignored from M-l, M-u and M-d, is actually important because it can significantly modify the smallest lepton flavor mixing angle theta(13) or three quark flavor mixing angles. (c) 2010 Elsevier B.V. All rights reserved.