Impact of vector new physics couplings on $B_s \to (K,\,K^{\ast})τν$ and $B \to πτν$ decays

Abstract: Experimental measurements of $R_{D}$, $R_{D^*}$ and $R_{J/\Psi}$ in $B \to (D,\,D^{\ast})l\nu$ and $B_c \to J/\Psi l \nu$ decays mediated via $b \to c\,l\,\nu$ charged current interactions deviate from standard model prediction by $2.3\sigma$, $3.4\sigma$ and $2\sigma$, respectively. In addition, a deviation of $1.5\sigma$ from the standard model prediction has been witnessed in $\mathcal B(B \to \tau \nu)$ mediated via $b \to u\,l\,\nu$ charged current interactions as well. Motivated by the anomalies present in $B$ and $B_c$ meson decays, we analyze the corresponding $B_s \to (K,\,K^{\ast})\,\tau\,\nu$ and $B \to \pi\tau\nu$ semileptonic decays within the standard model and beyond. We use an effective field theory formalism in which $b \to c$ and $b \to u$ semileptonic decays are assumed to exhibit similar new physics patterns. We give the predictions of various observables such as the branching fractions, ratio of branching ratios, lepton side forward backward asymmetry, lepton polarization fraction and convexity parameter for $B_s \to (K,\,K^{\ast})\tau \nu$ and $B \to \pi\tau\nu$ decay channels within the standard model and within various NP scenarios.