D*Dπ andB*Bπ couplings in QCD

Abstract

We calculate the ${\mathit{D}}^{\mathrm{*}}$Dπ and ${\mathit{B}}^{\mathrm{*}}$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 ${\mathit{g}}_{\mathit{D}}^{\mathrm{*}}$Dπ=12.5±1 and ${\mathit{g}}_{\mathit{B}}^{\mathrm{*}}$Bπ=29±3. From this we predict the partial width Γ(${\mathit{D}}^{\mathrm{*}+}$→${\mathit{D}}^0$ ${\mathrm{\pi }}^{+}$)=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 ${\mathit{g}}_{\mathit{B}}^{\mathrm{*}}$Bπ and ${\mathit{g}}_{\mathit{D}}^{\mathrm{*}}$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.