Solutions to $R_D$-$R_{D^*}$ in light of Belle 2019 data

Earlier this year, the Belle collaboration presented their new measurements of $R_D$ and $R_{D^*}$ using a new method. These measurements are consistent with the Standard Model predictions, whereas the global averages of the earlier measurements had a $4.1σ$ discrepancy. With the inclusion of the new data in the global averages, the discrepancy comes down to $3.1σ$. In this work, we study the study the new physics solutions to the $R_D$-$R_{D^*}$ anomaly allowed by the reduction in the discrepancy. Among the four fermion operators, which arise through a single particle exchange, only the $(V-A)$ operator solution survives. We found three additional solutions with two dis-similar operators. The branching ratio of $B_c\rightarrow τ\,\barν$ is powerful discriminant between these four allowed solutions.

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