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 ττ physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the ττ lepton probe the structure of the weak currents and the universality of their couplings to the WW boson. The universality of the leptonic ZZ couplings has also been tested through Z→ℓ+ℓ−Z→ℓ+ℓ− decays. The hadronic ττ 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 VusVus have been obtained with ττ data. The large mass of the ττ 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 ττ decays. Related subjects such as μμ decays, the electron and muon anomalous magnetic moments, neutrino mixing and BB-meson decays into ττ leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the ττ 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.