Probing new physics in $B_s\to (K,K^{\ast })\tau \nu$ and $B\to \pi \tau \nu$ decays

Motivated by the anomalies present in $b\to u$ and $b\to c$ semileptonic decays, we study the corresponding $B_s\to (K,K^{\ast })\tau \nu$ and $B \to \pi \tau \nu$ decays within an effective field theory formalism. Our analysis is based on a strict model dependent assumption, i.e., we assume that $b\to u$ and $b\to c$ transition decays exhibit similar new physics pattern. We give prediction of various observables such as the branching fraction, ratio of branching ratio, lepton side forward-backward asymmetry, longitudinal polarization fraction of the charged lepton and convexity parameter in the standard model and in the presence of vector type new physics couplings.