Charged Higgs boson contribution to $B_q^{-}\to \ell \bar{\nu }$ and $\bar{B}\to (P,V)\ell \bar{\nu }$ in a generic two-Higgs doublet model

Abstract

We comprehensively study the charged-Higgs contributions to the leptonic $B_q^{-}\to \ell \bar{\nu }$ ($q=u,c$) and semileptonic $\bar{B}\to X_q\ell \bar{\nu }$ ($X_u=\pi ,\rho ;X_c=D,D^{\ast }$) decays in the type-III two-Higgs-doublet model (2HDM). We employ the Cheng-Sher ansatz to suppress the tree-level flavor-changing neutral currents (FCNCs) in the quark sector. When the strict constraints from the $\Delta B=2$ and $b\to s\gamma$ processes are considered, parameters ${\chi }_{tq}^u$ from the quark couplings and ${\chi }_{\ell }^{\ell }$ from the lepton couplings dictate the leptonic and semileptonic $B$ decays. It is found that when the measured $B_u^{-}\to \tau \bar{\nu }$ and indirect bound of $B_c^{-}\to \tau \bar{\nu }$ obtained by LEP1 data are taken into account, $R(D)$ and $R(\pi )$ can have broadly allowed ranges; however, the values of $R(\rho )$ and $R(D^{\ast })$ are limited to approximately the standard model (SM) results. We also find that the same behaviors also occur in the $\tau$-lepton polarizations and forward-backward asymmetries ($A_{FB}^{X_q,\tau }$) of the semileptonic decays, with the exception of $A_{FB}^{D^{\ast },\tau }$, for which the deviation from the SM due to the charged-Higgs effect is still sizable. In addition, the $q^2$-dependent $A_{FB}^{\pi ,\tau }$ and $A_{FB}^{D,\tau }$ can be very sensitive to the charged-Higgs effects and have completely different shapes from the SM.

Comments: 53 pages, 13 figures, version accepted for publication in Physical Review D