New approach to the universal form factors in decays of heavy quarks

New results on current-induced transitions between heavy mesons are presented. In the heavy-quark limit of QCD, consistency relations fixing the relative q2-dependence of different hadronic form factors arise. With the help of these relations, we investigate to what extent the spin-flavour symmetry that QCD exhibits in the limit of infinite quark masses is broken in anti B → D(*) transitions. We develop a method to express the universal functions, that appear in leading and next-to-leading order in the 1/mQ expansion of current matrix elements, in terms of hadronic form factors evaluated at maximum recoil. In turn, the heavy-quark symmetries impose constraints on these form factors. To illustrate the application of our formalism and the kind of constraints it yields, the general results are evaluated within the framework of a particular model. Some phenomenological applications are discussed in detail. (orig.)