Precision tau physics

Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of τ physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the τ lepton probe the structure of the weak currents and the universality of their couplings to the W boson. The universality of the leptonic Z couplings has also been tested through Z → ℓ + ℓ − decays. The hadronic τ decay modes constitute an ideal tool for studying low-energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the Cabibbo mixing V u s have been obtained with τ data. The large mass of the τ opens the possibility to study many kinematically-allowed exclusive decay modes and extract relevant dynamical information. Violations of flavour and CP conservation laws can also be searched for with τ decays. Related subjects such as μ decays, the electron and muon anomalous magnetic moments, neutrino mixing and B -meson decays into τ leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the τ lepton is playing now a very important role at the LHC as a tool to test the Higgs properties and search for new physics at higher scales.