D*D pi and B*B pi couplings in QCD.

We calculate the D*Dπ and B*Bπ couplings using QCD sum rules on the light cone. 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 gD*Dπ=12.5±1 and gB*Bπ=29±3. From this we predict the partial width Γ(D*+→D0π+)=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 gB*Bπ and gD*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 ligh-cone sum rules.