| Summary: | We have derived constraints on the tau neutrino mass and fourth generation mixing from an analysis of the partial widths of tau lepton decays, in particular: τ̅→e̅ν<sup>-</sup>eντ, τ̅→μ̅ν<sup>-</sup>μντ, τ →π̅ντ, and τ →K̅ντ. We present predictions for the tau decay widths, allowing for a non-zero tau neutrino mass, mντ, and for mixing with a neutrino of mass mνL > MZ/2, which is parametrised using a Cabibbo-like mixing angle, ΘL. By comparison of these theoretical predictions with the experimental measurements, we obtain the following bounds at the 90% confidence level: mντ < 42 MeV and sin<sup>2</sup> ΘL < 0.014.
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