Symmetry and Neutrino Masses and Mixings

Based on a universal seesaw mass matrix model with three scalars φi, and by assuming an S3 flavor symmetry for the Yukawa interactions, the lepton masses and mixings are investigated systematically. In order to understand the observed neutrino mixing, the charged leptons (e, μ, τ) are regarded as the 3 elements (e1, e2, e3) of S3, while the neutrino masseigenstates are regarded as the irreducible representation (νη, νσ, νπ) of S3, where (νπ, νη) and νσ are a doublet and a singlet, respectively, which are composed of the 3 elements (ν1, ν2, ν3) of S3.