A current algebra sum rule for inclusive decays \bar B --> D + X + \ell + \bar \nu by Bjorken et al. is used to obtain constraints on the Isgur-Wise function \xi(\omega) for \bar B --> D \ell \bar \nu decays.
Cite
@article{arxiv.hep-ph/9809303,
title = {Constraint on the Isgur-Wise function for \bar B --> D semileptonic decays},
author = {Antonio O. Bouzas and Virendra Gupta},
journal= {arXiv preprint arXiv:hep-ph/9809303},
year = {2008}
}