# Revisiting the new-physics interpretation of the $b\to c\tau\nu$ data

## TL;DR

This paper reevaluates new-physics explanations for anomalies in semileptonic B decays, incorporating recent Belle data, and identifies key observables that can distinguish among different theoretical models.

## Contribution

It provides an updated analysis of new-physics scenarios explaining B decay anomalies, highlighting the roles of various operators and the importance of specific measurements.

## Key findings

- Left-handed currents and tensor contributions are favored explanations.
- Pure right-handed and scalar models are disfavored by collider and lifetime constraints.
- Tau polarization measurements can effectively discriminate among new-physics scenarios.

## Abstract

We revisit the status of the new-physics interpretations of the anomalies in semileptonic $B$ decays in light of the new data reported by Belle on the lepton-universality ratios $R_{D^{(*)}}$ using the semileptonic tag and on the longitudinal polarization of the $D^*$ in $B\to D^*\tau\nu$, $F_L^{D^*}$. The preferred solutions involve new left-handed currents or tensor contributions. Interpretations with pure right-handed currents are disfavored by the LHC data, while pure scalar models are disfavored by the upper limits derived either from the LHC or from the $B_c$ lifetime. The observable $F_L^{D^*}$ also gives an important constraint leading to the exclusion of large regions of parameter space. Finally, we investigate the sensitivity of different observables to the various scenarios and conclude that a measurement of the tau polarization in the decay mode $B\to D\tau\nu$ would effectively discriminate among them.