Charged-Higgs on R_D^(*), τ polarization, and FBA

We study the influence of a charged-Higgs on the excess of branching fraction ratio, R_M = BR(anti B → Mτ anti ν_τ)/BR(anti B → Ml anti ν_l) (M = D, D*), in a generic two-Higgs-doublet model. In order to investigate the lepton polarization, the detailed decay amplitudes with lepton helicity are given. When the charged-Higgs is used to resolve excesses, it is found that two independent Yukawa couplings are needed to explain the R_D and R_D* anomalies. We show that when the upper limit of BR(B_c → τ anti ν_τ) < 30% is included, R_D can be significantly enhanced while R_D* < 0.27. With the BR(B_c → τ anti ν_τ) constraint, we find that the τ-lepton polarizations can be still affected by the charged-Higgs effects, where the standard model (SM) predictions are obtained: P^τ_D ∼ 0.324 and P^τ_D* ∼ -0.500, and they can be enhanced to be P^τ_D ∼ 0.5 and P^τ_D* ∼ -0.41 by the charged-Higgs. The integrated lepton forward-backward asymmetry (FBA) is also studied, where the SM result is anti A^D(*),τ_FB ∼ -0.359(0.064), and they can be enhanced (decreased) to be anti A^D(*),τ_FB ∼ -0.33(0.02). (orig.)