PERMUTATION SYMMETRY AND THE ORIGIN OF FERMION MASS HIERARCHY

A realization of the flavor-democracy approach to quark and lepton masses is provided in the context of the standard model with a horizontal S3 permutation symmetry. In this model, t and b quarks pick up mass at the tree level, c, s-quark and -lepton masses arise at the one-loop level, u, d, and 1/4 masses at the two-loop level, and the electron mass at the three-loop level, thus reproducing the observed hierarchial structure without fine tuning of the Yukawa couplings. The pattern of quark mixing angles also emerges naturally, with Vus,VcbO(μ), VubO(μ2), where μ is a loop expansion parameter. © 1990 The American Physical Society.