Physical Implications of a Vector-like Extension of the Standard Model
  Physical implications of a vector-like extension of the standard model for heavier quarks and leptons with $SU(2)\times U(1)$ gauge symmetry and only one Higgs doublet are discussed. This scheme incorporates infinitely many fermions, and the chiral structure is realized by a non-vanishing analytic index of mass matrices. The model is perturbatively well controllable, and the physical Higgs particle generally mediates leptonic as well as quark flavor-changing processes at a rate below the present experimental limit. This model illustrates a general feature of models where some of the fermion masses are of non-Higgs origin. 
Kazuo Fujikawa (Dept. of Physics, Univ. of Tokyo)