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

TL;DR

This paper performs a model-independent analysis of $b o (c, u) au u$ decays, exploring new physics effects to explain deviations from the Standard Model in branching ratios and related observables.

Contribution

It introduces a comprehensive effective Lagrangian approach to constrain new physics couplings using recent experimental data and proposes new observables to better understand potential new physics effects.

Findings

Constraints on new physics couplings from $R_D$, $R_{D^{ ext{*}}}$, and related ratios.

Impact of new physics on $B_s o (D_s, D_s^{ ext{*}}) au u$ and $B o \pi au u$ decay observables.

Potential explanations for deviations from Standard Model expectations.

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.