Exclusive weak B decays involving $\tau$ lepton in the relativistic   quark model
  Semileptonic and leptonic B decays are analyzed in the framework of the relativistic quark model. Special attention is payed to the decays involving $\tau$ lepton. It is found that the calculated particular decay branching fractions are consistent with available experimental data within error bars. However, the predicted and recently measured ratios $R(D^{(*)})$ of the $B\to D^{(*)}\tau\nu_\tau$ and $B\to D^{(*)}l\nu_l$ branching fractions differ by 1.75$\sigma$ for $R(D)$ and by 2.4$\sigma$ for $R(D^*)$. 
R. N. Faustov, V. O. Galkin
hep-ph hep-ex