Signature of lepton flavor universality violation in Bs→Dsτν semileptonic decays

Abstract

Deviation from the standard model prediction is observed in many semileptonic $B$ decays mediated via $b\ensuremath{\rightarrow}c$ charged current interactions. In particular, current experimental measurements of the ratio of branching ratio ${R}_{D}$ and ${R}_{{D}^{*}}$ in $B\ensuremath{\rightarrow}{D}^{(*)}l\ensuremath{\nu}$ decays disagree with standard model expectations at the level of about $4.1\ensuremath{\sigma}$. Moreover, the recent measurement of the ratio of branching ratio ${R}_{J/\mathrm{\ensuremath{\Psi}}}$ by LHCb, where ${R}_{J/\mathrm{\ensuremath{\Psi}}}=\mathcal{B}({B}_{c}\ensuremath{\rightarrow}J/\mathrm{\ensuremath{\Psi}}\ensuremath{\tau}\ensuremath{\nu})/\mathcal{B}({B}_{c}\ensuremath{\rightarrow}J/\mathrm{\ensuremath{\Psi}}\ensuremath{\mu}\ensuremath{\nu})$, is more than $2\ensuremath{\sigma}$ away from the standard model prediction. In this context, we consider an effective Lagrangian in the presence of vector and scalar new physics couplings to study the implications of ${R}_{D}$ and ${R}_{{D}^{*}}$ anomalies in ${B}_{s}\ensuremath{\rightarrow}{D}_{s}\ensuremath{\tau}\ensuremath{\nu}$ decays. We give a prediction of several observables such as the branching ratio, ratio of branching ratio, forward backward asymmetry parameter, $\ensuremath{\tau}$ polarization fraction, and convexity parameter for the ${B}_{s}\ensuremath{\rightarrow}{D}_{s}\ensuremath{\tau}\ensuremath{\nu}$ decays within the standard model and within various new physics scenarios.