Factors in Light-Cone Sum Rules and the D-Meson Distribution Amplitude

We calculate the weak form factors of the decays B_c(B)\to Dlύ by using the chiral current orrelator within the framework of the QCD light-cone sum rules (LCSRs). The expressions of the form factors only depend on the leading twist distribution amplitude (DA) of the D meson. Three models of the D-meson distribution amplitude are employed. Our prediction, by using the D-meson distribution amplitude with the exponential suppression at the end points, favours the three-points sum rule (3PSR) approach with the Coulomb corrections included, and is compatible with other approaches.