Semitauonic B Decay Anomaly

The anomalously large experimentally measured ratios of the semitauonic decay $B\rightarrow D^{(*)} +\tau+\nu$ and the corresponding semileptonic $B\rightarrow D^{*} +\l+\bar{\nu}_l$ disagree with the predictions of the standard E.W + QCD model(S.M). We briefly comment on this disagreement and on possible new physics explanations which are rather constrained and difficult to implement.