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

## TL;DR

This paper analyzes the updated $R_D$ and $R_{D^*}$ measurements from Belle 2019 data, identifying viable new physics solutions and emphasizing the role of $B_c
ightarrow au ar{
u}$ decay as a discriminant.

## Contribution

It identifies the surviving new physics solutions to the $R_D$-$R_{D^*}$ anomaly after recent Belle data updates, highlighting the importance of specific fermion operators.

## Key findings

- Only the $(V-A)$ operator solution remains viable.
- Three additional solutions involve two dis-similar operators.
- $B_c
ightarrow au ar{
u}$ decay is a key discriminant.

## Abstract

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 $4.1\sigma$ 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 $R_D$-$R_{D^*}$ 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 $B_c\rightarrow \tau\,\bar{\nu}$ is powerful discriminant between these four allowed solutions.