Constraints on the tau neutrino mass and mixing from precise measurements of tau decay rates

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: τ−→ e−ν̄eντ , τ −→μ−ν̄μντ , τ →π −ντ , and τ →K −ντ . 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 < 42MeV and sin 2 θL < 0.014.