Heavy quark expansion and universal form factors in quark model

Abstract

Meson transition amplitudes of the vector, axial-vector, and tensor quark currents are analyzed within dispersion formulation of the constituent quark model. The form factors in the decay region are given by relativistic double spectral representations through the wave functions of the inital and final mesons. We perform heavy quark expansion of the quark-model mesonic matrix elements with a next-to-leading order accuracy and demonstrate that matching this expansion to the heavy-quark expansion in QCD requires subtractions in the double spectral representations for the form factors and allows fixing the subtraction terms. The Isgur-Wise function and next-to-leading order universal form factors are calculated.