Results on the Lorentz structure of tau decays

Summary

Tau decays are well described by the Standard Model, but precision tests of τ decay properties could also open a window to new physics. Since the four-fermion coupling approximation holds well even for the heavy τ lepton, a general ansatz for its leptonic decays (following Michel) and for semi-hadronic decays offers well-defined parameters describing the Lorentz structure of the interaction. These parameters have been determined at several detectors. Recent measurements at DORIS and LEP give results with improved precision, and allow first constraints on non-standard interactions.