IS THERE ANY EVIDENCE FOR A HEAVY NEUTRAL FERMION (V(TAU)R)

In the standard model a right-handed neutrino can appear only by mixing with the left-handed neutrinos. Precise electroweak data constrain this mixing. We consider models in which the mixing is not proportional to neutrino masses. We have analyzed data and constraints on m(t), m(H) with and without mixing (sin-epsilon) of neutrinos with new inert fermions. For universal nu-mixing, sin-epsilon = 0.09; if only nu-tau mixes, sin-epsilon-tau = 0.22. Thus nu-tau-data, GAMMA-tau and GAMMA-Z-inv, if interpreted without caution, perhaps favor a nonzero nu-tau-mixing and the existence of heavy neutral fermions.