New physics in inclusive $B \to X_c\ell \bar{\nu}$ decay in light of $R(D^{(*)})$ measurements

Abstract

In this work we study the effects of new-physics (NP) operators with different Lorentz structures on the inclusive $B \to X_c\tau \bar{\nu}$ decay and make predictions for the ratio of total decay rates $R(X_c)=\frac{\Gamma(B \to X_c\tau \bar{\nu}_\tau)}{\Gamma(B \to X_c \ell \bar{\nu}_\ell)}$ with $\ell=e, \mu$, the differential decay rates, $\frac{d\Gamma}{dq^2}$ and $\frac{d\Gamma}{dE_\tau}$, forward-backward asymmetry $A_{FB}$ and the ratio of the differential decay rates $B(q^2)=\frac{d\Gamma(B \to X_c\tau \bar{\nu}_\tau)/dq^2}{d\Gamma(B \to X_c \ell \bar{\nu}_\ell)/dq^2}$. In addition, we introduce some leptoquark models as explicit models of the NP operators and study their effects on the inclusive decay. We consider $\mathcal{O}(\alpha_s)$ radiative and $1/m_b$ nonperturbative corrections to the Standard Model (SM) decay rate and ignore their small effects in the NP contributions.