Beyond $\mathcal{R}(D^{(*)})$ with the general 2HDM-III for $b\to c\tau\nu$

TL;DR

This paper investigates the parameter space of the general 2HDM-III model in light of current measurements of $ drstar$ and related observables, predicting potential signals and constraints for future experiments.

Contribution

It provides a comprehensive analysis of scalar and pseudoscalar couplings in the 2HDM-III, linking experimental data to model parameters and predicting additional observables.

Findings

Allowed parameter regions are consistent with current measurements.

The model could be ruled out if future measurements confirm a large $ jpsi$.

Predicted observables include differential decay rates and tau polarizations.

Abstract

We review the parameter regions allowed by measurements of $\mathcal{R}(D^{(*)})$ and by a theoretical limit on ${\cal B}(B_{c}\to\tau\nu)$ in terms of generic scalar and pseudoscalar new physics couplings, $g_s$ and $g_p$. We then use these regions as constraints to predict the ranges for additional observables in $b\to c\tau\nu$ including the differential decay distributions $d\Gamma/dq^{2}$; the ratios $\mathcal{R}(J/\psi)$ and $\mathcal{R}(\Lambda_{c})$; and the tau-lepton polarisation in $B\to D^{(\star)}\tau\nu$, with emphasis on the CP violating normal polarisation. Finally we map the allowed regions in $g_s$ and $g_p$ into the parameters of four versions of the Yukawa couplings of the general 2HDM-III model. We find that the model is still viable but could be ruled out by a confirmation of a large $\mathcal{R}(J/\psi)$.