Is there any evidence for a heavy neutral fermion (ν(τ)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 ${\mathit{m}}_{\mathit{t}}$,${\mathit{m}}_{\mathit{H}}$ with and without mixing (sinε) of neutrinos with new inert fermions. For universal ν mixing, sinε=0.09; if only ${\nu }_{\mathrm{\tau }}$ mixes, sin${\mathrm{\epsilon }}_{\mathrm{\tau }}$=0.22. Thus ${\nu }_{\mathrm{\tau }}$ data, Γτ and ${\mathrm{\Gamma }}_{\mathit{Z}}^{\mathrm{inv}}$, if interpreted without caution, perhaps favor a nonzero ${\nu }_{\mathrm{\tau }}$ mixing and the existence of heavy neutral fermions.