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 generationmixing from an analysis of the partial widths of tau lepton decays, inparticular: tau -> e nu nu_tau, tau -> mu nu nu_tau, tau -> pi nu_tau, tau -> Knu_tau. We present predictions for the tau decay widths, allowing for anon-zero tau neutrino mass, m(nu_tau), and for mixing with a neutrino of massm(nu_L) > M_Z/2, which is parametrised using a Cabibbo-like mixing angle,theta_L. By comparison of these theoretical predictions with the experimentalmeasurements, we obtain the following bounds at the 90% confidence level:m(nu_tau) < 42 MeV and sin^2(theta_L) < 0.014.Comment: 11 pages, 2 figure