Nondecoupling of Heavy Fermions and a Special Yukawa Texture

Talk based on work entitled “Yukawa textures, new physics and nondecoupling,” done in collaboration with G. C. Branco and J. I. SilvaMarcos, arXiv:hep-ph/0612252, to appear in Phys. Rev. D. In this work we pointed out that New Physics can play an important rôle in rescuing some of the Yukawa texture zero ansätze which would otherwise be eliminated by the recent, more precise measurements of VCKM . We have shown that the presence of an isosinglet vector-like quark which mixes with standard quarks, can render viable a particularly interesting four texture zero Yukawa ansatz. The crucial point is the nondecoupling of the effects of the isosinglet quark, even for arbitrary large values of its mass.