Analysis of $b\rightarrow c\tau\bar{\nu}_\tau$ anomalies using weak effective Hamiltonian with complex couplings

TL;DR

This paper investigates anomalies in $b\rightarrow c\tau\bar{\nu}_\tau$ decays by extending the Standard Model with complex effective operators, analyzing their effects on observables, and proposing correlations and predictions to distinguish new physics scenarios.

Contribution

It introduces complex Wilson coefficients for vector, scalar, and tensor operators in the weak effective Hamiltonian to explain current anomalies and derives sum rules linking various observables.

Findings

Identifies parameter space of new physics couplings consistent with anomalies.

Predicts values of $R_{\tau/\ell}(\Lambda_c)$, $R_{\tau/\mu}(J/\psi)$, and $R_{\tau/\ell}(X_c)$.

Analyzes correlations and impacts of new couplings on angular and CP asymmetries.

Abstract

Recently, the experimental measurements of the branching ratios and different polarization asymmetries for the processes occurring through flavor-changing-charged current $b\rightarrow c\tau\overline{\nu}_{\tau}$ transitions by BABAR, Belle, and LHCb show some sparkling differences with the corresponding SM predictions. Assuming the left handed neutrinos, we add the dimension-six vector, (pseudo-)scalar, and tensor operators with complex WCs to the SM WEH. Together with 60%, 30% and 10% constraints coming from the branching ratio of $B_{c}\to\tau\bar{\nu}_{\tau}$, we analyze the parametric space of these new physics WCs accommodating the current anomalies in the purview of the most recent HFLAV data of $R_{\tau/{\mu,e}}\left(D\right)$, $R_{\tau/{\mu,e}}\left(D^*\right)$ and Belle data of $F_{L}\left(D^*\right)$ and $P_{\tau}\left(D^*\right)$. Furthermore, we derive the sum rules which correlate these observables with $R_{\tau/{\mu,e}}\left(D\right)$ and $R_{\tau/{\mu,e}}\left(D^*\right)$. Using the best-fit points of the new complex WCs along with the latest measurements of $R_{\tau/{\mu,e}}\left(D^{(*)}\right)$, we predict the numerical values of the observable $R_{\tau/\ell}\left(\Lambda_c\right)$, $R_{\tau/\mu}\left(J/\psi\right)$ and $R_{\tau/\ell}\left(X_c\right)$ from the sum rules. Apart from finding the correlation matrix among the observables under consideration, we plot them graphically which is useful to discriminate different NP scenarios. Finally, we study the impact of these NP couplings on various angular and the CP triple product asymmetries, that could be measured in some ongoing and future experiments. The precise measurements of these observables are important to check the SM and extract the possible NP.