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

Abstract

Stringent relations between the $B^{(\ast )}\to D^{(\ast )}$ 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 $B\to D^{(\ast )}\ell \nu$ with model-independent parametrizations and in the related prediction of $R(D^{(\ast )})$. 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 $R(D^{\ast })=0.260(8)$.

Comments: 13 pages. Improved discussion of R(D*), P_tau prediction and various explanations added