Recent results in semileptonic B decays at LHCb

The Standard Model (SM) predicts the universality of lepton couplings with the electroweak gauge bosons. Three measurements performed by the LHCb collaboration using semitauonic $B$ decays are reported in this work: a combined measurement of $R(D^0)$ and $R(D^*)$ using muonic $\tau$ decays, a measurement of $R(D^*)$ using hadronic $\tau$ decays and the first measurement of the longitudinal $D^*$ polarization fraction ($F_L^{D^*}$) in the same $\tau$ decay channel. Including these latest LHCb results, the updated world average of the $R(D)-R(D^*)$ combination shows a discrepancy of 3.3 standard deviations with respect to the SM prediction. The value of $F_L^{D^*}$ is found to be compatible with the SM.