ISGUR-WISE FUNCTION FROM BETHE-SALPETER AMPLITUDE

We develop the improved ladder approximation to QCD in order to apply it to the heavy quark mesons. The resulting Bethe-Salpeter equation is expanded in powers of the inverse heavy quark mass 1/M, and is shown to be consistent with the heavy quark spin symmetry. We calculate nume rically the universal leading order BS amplitude for heavy pseudoscala r and vector mesons, and use this to evaluate the Isgur-Wise function and the decay constant F(B). The resulting Isgur-Wise function predict s a large charge radius, rho2 = 1.8-2.0, which when fitted to the ARGU S data corresponds to the value V(cb) = .044-.050 for the Kobayashi-Ma skawa matrix element.