Recent results from LHCb on semileptonic decays of b-hadrons

Recent results on semileptonic decays of $b$ hadrons at LHCb are presented, with particular emphasis on decays involving $\tau$ leptons in the final state. A new measurement of $\mathscr{R}(D^{*-} \equiv \mathscr{B}(B^0 \to D^{*-} \tau^+ \nu_{\tau}/ \mathscr{B}(B^0 \to D^{*-} \mu^+ \nu_{\mu})$ is reported, by using for the first time the $\tau$ lepton decays with three charged pions in the final state. A value of $\mathscr{R}(D^{*-})=0.285 \pm 0.019 \pm0.025 \pm 0.013$ is obtained, where the the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of external branching fractions. This measurement is in agreement with the Standard Model prediction and with previous results.