Measurements of lepton universality at LHCb

Lepton universality violation would represent a signal of physics beyond the Standard Model. Anomalies have been observed in the measurement of the branching ratios of semileptonic decays of beauty mesons in third-generation leptons. This contribution reports on the measurements of the observable $R(D^{\ast -}) = B(B^0 \rightarrow D^{\ast -} \tau^+ \nu _\tau)/B(B^0 \rightarrow D^\ast - \mu^+ \nu_\mu)$ and $R(J/\psi)$ = $B(B^+_c \rightarrow J/\psi \tau^+ \nu_\tau)/B(B^+_c \rightarrow J/\psi \mu^+ \nu_\mu)$ performed at LHCb with data collected during the Run 1 of the LHC.