$tau$ physics at LHCb

We report on the first searches for lepton flavour violating $tau^-$ decays at a hadron collider. These include searches for the lepton flavour violating decay $tau^-to mu^+mu^-mu^-$ and the lepton flavour and baryon number violating decays $tau^-to bar{p}mu^+mu^-$ and $tau^-to pmu^-mu^-$. Upper limits of ${cal B}(tau^-to mu^+mu^-mu^-) < 4.6 times 10^{-8}$, ${cal B}(tau^-to bar{p}mu^+mu^-) < 3.4 times 10^{-7}$ and ${cal B}(tau^-to pmu^-mu^-) < 4.6 times 10^{-7}$ are set at 90% confidence level. A measurement of the inclusive $Ztotau^+tau^-$ cross-section at 7 TeV is also reported and is found to be consistent with the Standard Model. The ratio of the $Ztotau^+tau^-$ cross-section to the $Ztomu^+mu^-$ cross-section is found to be consistent with lepton universality.