Top quark, heavy fermions and the composite Higgs boson

We study the properties of heavy fermions in the vector-like representation of the electroweak gauge group SU(2)w x U(l)(Y) with Yukawa couplings to t he standard model Higgs boson. Applying the renormalization group analysis, we discuss the effects of heavy fermions to the vacuum stability bound and the triviality bound on the mass of the Higgs boson. We also discuss the i nteresting possibility that the Higgs particle is composed of the top quark and heavy fermions. The bound on the composite Higgs mass is estimated usi ng the method of Bardeen, Hill and Lindner (Phys. Rev. D41 (1990) 1647), 15 0 GeV less than or equal to m(H) less than or equal to 450 GeV.