Dispersive bounds on the shape of B → D(∗)l v form factors Original Research Article

Dispersive constraints on the shape of the form factors which describe the exclusive decays B → D(∗)l v are derived fully exploiting spin symmetry in the ground-state doublet of heavy-light mesons. The analysis includes all twenty B(∗) → D(∗) semileptonic form factors. Heavy-quark symmetry, with both short-distance and 1/mQ corrections included, is used to provide relations between the form factors near zero recoil. Simple one-parameter functions are derived, which describe the form factors in the semileptonic region with an accuracy of better than 2%. The implications of our results for the determination of ∥Vcb∥ are discussed.