Form Factors of Semileptonic M L3 Decays *

We study in detail the kinematics of semileptonic M l3 (M → M ′ lν) decay, considering only the new models preserving all the gauge symmetries of the Standard Model (SM), and assuming that neutrinos are massless and left-handed as in the SM. And we present a brief review of the recent theoretical progress on model independent constraints on the form factors of M l3 decays using dispersion relations. Finally we review a new parton model approach for semileptonic B → D(D *)lν decays, by extending the inclusive parton model and by combining with the results of the heavy quark effective theory. We also obtain the slope of the Isgur-Wise function.