$R(D^*)$, $|V_{cb}|$, and the Heavy Quark Symmetry relations between form factors

Stringent relations between the $B^{(*)} to 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 $Bto D^{(*)}ell u$ with model-independent parametrizations and in the related prediction of $R(D^{(*)})$. We find $|V_{cb}|=41.5(1.3) 10^{-3}$ and $|V_{cb}|=40.6(^{+1.2}_{-1.3}) 10^{-3}$ using input from Light Cone Sum Rules, and $R(D^{*})=0.260(8)$.