Resolving $R_D$ and $R_{D^{\ast }}$ anomalies

The current world averages of the ratios $R_{D^{(\ast )}}$ are about $4\sigma$ away from their Standard Model prediction. These measurements indicate towards the violation of lepton flavor universality in $b\to cl\bar{\nu }$ decay. The different new physics operators, which can explain the $R_{D^{(\ast )}}$ measurements, have been identified previously. We show that a simultaneous measurement of the polarization fractions of $\tau$ and $D^{\ast }$ and the angular asymmetries $A_{FB}$ and $A_{LT}$ in $B\to D^{\ast }\tau \bar{\nu }$ decay can distinguish all the new physics amplitudes and hence uniquely identify the Lorentz structure of new physics.