How to Evade a No-Go Theorem in Flavor Symmetries
  A no-go theorem in flavor symmetries is reviewed. The theorem asserts that we cannot bring any flavor symmetry into mass matrix model in which number of Higgs scalars is, at most, one for each sector (e.g. H_u and H_d for up- and down-quark sectors, respectively). Such the strong constraint comes from the SU(2)_L symmetry. Possible three options to evade the theorem are discussed. 
Yoshio Koide