| Summary: | Abstract As a consequence of the Ward identity for hadronic matrix elements, we find relations between the differential decay rates of semileptonic decay modes with the underlying quark-level transition b → cτν, which are valid in scalar models. The decay-mode dependent scalar form factor is the only necessary theoretical ingredient for the relations. Otherwise, they combine measurable decay rates as a function of the invariant mass-squared of the lepton pair q 2 in such a way that a universal decay-mode independent function is found for decays to vector and pseudoscalar mesons, respectively. This can be applied to the decays B → D ∗ τv , B s → D s ∗ τv , B c → J / ψτv $$ B\to {D}^{\ast}\tau v,{B}_s\to {D}_s^{\ast}\tau v,{B}_c\to J/\psi \tau v $$ and B → Dτv, B s → D s τv, B c → η c τv, with implications for R(D (*)), R D s ∗ $$ R\left({D}_s^{\left(\ast \right)}\right) $$ , R(J/ψ), R(η c ), and ℬ(B c → τv). The slope and curvature of the characteristic q 2-dependence is proportional to scalar new physics parameters, facilitating their straight forward extraction, complementary to global fits.
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