We calculate the D * Dπ and B * Bπ couplings using QCD sum rules on the lightcone. In this approach, the large-distance dynamics is incorporated in a set of pion wave functions. We take into account two-particle and three-particle wave functions of twist 2, 3 and 4. The resulting values of the coupling constants are g D * Dπ = 12.5 ± 1 and g B * Bπ = 29 ± 3. From this we predict the partial width Γ(D * + → D 0 π + ) = 32 ± 5 keV . We also discuss the soft-pion limit of the sum rules which is equivalent to the external axial field approach employed in earlier calculations. Furthermore, using g B * Bπ and g D * Dπ the pole dominance model for the B → π and D → π semileptonic form factors is compared with the direct calculation of these form factors in the same framework of light-cone sum rules.
We calculate the form factors for the heavy-to-light transitions B → π, K by means of QCD sum rules using π and K light-cone wave functions. Higher twist contributions as well as gluonic corrections are taken into account. The sensitivity to the shape of the leading-twist wave functions and effects of SU(3)-breaking are discussed. The results are compared with quark model predictions and with the results from QCD sum rules for three-point correlators.
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