Uraltsev sum rule in Bakamjian-Thomas quark models

We show that the sum rule recently proved by Uraltsev in the heavy quark li mit of QCD holds in relativistic quark models la Bakamjian and Thomas, that were already shown to satisfy Isgur-Wise scaling and Bjorken sum rule. Thi s new sum rule provides a rationale for the lower bound of the slope of the elastic IW function rho (2) greater than or equal to 3/4 obtained within t he BT formalism some years ago. Uraltsev sum rule suggests an inequality \ tau (3/2) (1)\ > \ tau (1/2) (1)\. This difference is interpreted in the BT formalism as due to the Wigner rotation of the light quark spin, independe ntly of a possible LS force. In BT models, the sum rule convergence is very fast, the n = 0 state giving the essential contribution in most of the phe nomenological potential models. We underline that there is a serious proble m, in the heavy quark limit of QCD, between theory and experiment for the d ecays B --> D-0,D-1* (broad)lv, independently of any model calculation. (C) 2001 Published by Elsevier Science B.V.