New physics effects on $B\to D^{(*)}τν$ decays

Abstract

We investigate new physics effects on $B\to D^{(*)}τν$ decays in a general and model-independent way. The $χ^2$ fits for fractions of the branching ratios $R(D^{(*)})$ and other polarization parameters are implemented. We parameterize the relevant Wilson coefficients with a new physics scale and its power together with combined fermionic couplings. Constraints from $B_c\toτν$ are imposed such that its branching ratio is less than 30%. For a moderate range of our parameters we find that the new physics scale goes up to $\lesssim 27$ TeV for ordinary new particle contributions. It turns out that the polarization asymmetry of $τ$ for $B\to D$ transition can be negative only for a few combinations of the new physics operators. We also discuss related processes $B_c\to J/Ψτν$ and $Λ_b\toΛ_cτν$ decays.