Model independent analysis of $b \to (c,\,u)\,\tau\nu$ leptonic and semileptonic decays

Abstract

Latest measurement of the ratio of branching ratios $R_D = \mathcal B(B \to D\,\tau\,\nu)/\mathcal B(B \to D\,l\,\nu)$ and $R_{D^{\ast}} = \mathcal B(B \to D^{\ast}\,\tau\,\nu)/\mathcal B(B \to D^{\ast}\,l\,\nu)$, where $l$ is either an electron or muon, differs from the standard model expectation by $1.9\sigma$ and $3.3\sigma$, respectively. Similar tension has been observed in purely leptonic $B \to \tau\nu$ decays as well. In this context, we consider the most general effective Lagrangian in the presence of new physics and perform a model independent analysis to explore various new physics couplings. Motivated by the recently proposed new observables $R_D^{\tau} = R_D/\mathcal B(B \to \tau\nu)$ and $R_{D^{\ast}}^{\tau} = R_{D^{\ast}}/\mathcal B(B \to \tau\nu)$, we impose $2\sigma$ constraints coming from $R_D^{\tau}$ and $R_{D^{\ast}}^{\tau}$ in addition to the constraints coming from $R_D$, $R_{D^{\ast}}$, and $\mathcal B(B \to \tau\nu)$ to constrain the new physics parameter space. We study the impact of new physics on various observables related to $B_s \to (D_s,\,D^{\ast}_s)\tau\nu$ and $B \to \pi\tau\nu$ decay processes.