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

Abstract

Earlier this year, the Belle collaboration presented their new measurements of $R_D$ and $R_{D^{\ast }}$ using a new method. These measurements are consistent with the Standard Model predictions, whereas the global averages of the earlier measurements had a $4.1\sigma$ discrepancy. With the inclusion of the new data in the global averages, the discrepancy comes down to $3.1\sigma$. In this work, we study the study the new physics solutions to the $R_D$-$R_{D^{\ast }}$ 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 $B_c\to \tau \bar{\nu }$ is powerful discriminant between these four allowed solutions.

Comments: 6 pages, 2 figures, 4 tables, title changed