Impact of polarization observables and Bc→τν on new physics explanations of the b→cτν anomaly

The combined analysis of the BABAR, Belle, and LHCb data on B→Dτν, B→D*τν and Bc→J/Ψτν decay observables shows evidence of physics beyond the Standard Model (SM). In this article, we study all the one- and two-dimensional scenarios which can be generated by adding a single new particle to the SM. We put special emphasis on the model-discriminating power of FL(D*) and of the τ polarizations, and especially on the constraint from the branching fraction BR(Bc→τν). We critically review this constraint and do not support the aggressive limit of BR(Bc→τν)