LIGHT-QUARK DEPENDENCE OF THE ISGUR-WISE FUNCTION FROM QCD SUM-RULES

We study the light quark dependence of the Isgur-Wise function for B-a -->D-a and B-a-->D-a in the framework of QCD sum rules. At zero recoi l, all the Isgur-Wise functions are equal, as required by heavy quark symmetry, and at nonzero recoil the Isgur-Wise function for B, decay f alls faster than that for B-u,B-d decay, which is just contrary to the recent prediction of the heavy meson chiral perturbation theory. As a by-product we also estimate SU(3)-breaking effects in the mass and th e decay constant.