New constraints on the tau neutrino mass and fourth generation mixing

We present new constraints on the mass $m_{{\nu }_{\tau }}$ of the tau neutrino and its mixing with a fourth generation neutrino. From an analysis of the partial widths of tau lepton decays we obtain the following bounds at the 90% confidence level: $m_{{\nu }_{\tau }}<32$ MeV and ${\sin }^2\theta <0.007$, where $\theta$ describes the Cabibbo-like mixing of the third and fourth generation neutrinos.