Tau lepton physics: theory overview

The pure leptonic or semileptonic character of τ decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic τ decay modes constitute an ideal tool for studying low-energy effects of the strong interactions in very clean conditions; a well-known example is the precise determination of the QCD coupling from τ-decay data. New physics phenomena, such as a non-zero mντ or violations of (flavour/CP) conservation laws can also be searched for with τ decays. (orig.)