R(D^∗), |V_cb|, and the Heavy Quark Symmetry relations between form factors

Stringent relations between the B^(∗)→D^(∗) form factors exist in the heavy quark limit and the leading symmetry breaking corrections are known. We reconsider their uncertainty and role in the analysis of recent Belle data for B→D^(∗)ℓν with model-independent parametrizations and in the related prediction of R(D^(∗)). We find |V_cb|=41.5(1.3) 10⁻³ and |V_cb|=40.6(_−1.3^+1.2) 10⁻³ using input from Light Cone Sum Rules, and R(D^∗)=0.260(8).