Scalar contributions to b → c(u)τν transitions

We perform a comprehensive analysis of scalar contributions in b→cτν transitions including the latest measurements of R(D(⁎)), the q2 differential distributions in B→D(⁎)τν, the τ polarization asymmetry for B→D⁎τν, and the bound derived from the total width of the Bc meson. We find that scalar contributions with the simultaneous presence of both left- and right-handed couplings to quarks can explain the available data, specifically R(D(⁎)) together with the measured differential distributions. However, the constraints from the total Bc width present a slight tension with the current data on B→D⁎τν in this scenario, preferring smaller values for R(D⁎). We discuss possibilities to disentangle scalar new physics from other new-physics scenarios like the presence of only a left-handed vector current, via additional observables in B→D(⁎)τν decays or additional decay modes like the baryonic Λb→Λcτν and the inclusive B→Xcτν decays. We also analyze scalar contributions in b→uτν transitions, including the latest measurements of B→τν, providing predictions for Λb→pτν and B→πτν decays. The potential complementarity between the b→u and b→c sectors is finally investigated once assumptions about the flavour structure of the underlying theory are made.