Abstract
We revisit the calculation of the strong couplings D∗Dπ and B∗Bπ from the QCD light-cone sum rules using the pion light-cone distribution amplitudes. The accuracy of the correlation function, calculated from the operator product expansion near the light-cone, is upgraded by taking into account the gluon radiative corrections to the twist-3 terms. The double spectral density of the correlation function, including the twist-2, 3 terms at mathcal{O}left({alpha}_sright) and the twist-4 LO terms, is presented in an analytical form for the first time. This form allows us to use various versions of the quark-hadron duality regions in the double dispersion relation underlying the sum rules. We predict {g}_{D^{ast } Dpi}={14.1}_{-1.2}^{+1.3} and {g}_{B^{ast } Bpi}={30.0}_{-2.4}^{+2.6} when the decay constants of heavy mesons entering the light-cone sum rule are taken from lattice QCD results. We compare our results with the experimental value for the charmed meson coupling and with the lattice QCD calculations.
Highlights
Goes back to [17] where the pion-nucleon and ρωπ couplings were calculated
The LCSR predictions [13] for the D∗Dπ and B∗Bπ strong couplings at the leading order (LO) in αs are sensitive to the values of the pion distribution amplitudes (DAs) at u = u = 1/2 where u and u ≡ 1 − u are the fractions of the pion momentum carried by the collinear quark and antiquark in the two-parton state of the pion
Assessing the accuracy of the LCSR for the heavy-light strong couplings, one has to mention that the use of the double dispersion relation makes this sum rule more sensitive to the quark-hadron duality approximation than the LCSR for heavy-to-light form factors based on the single-variable dispersion relation
Summary
Hereafter we use a generic notation H(∗) for both pseudoscalar (vector) mesons D(∗) and B(∗). To derive LCSR for the strong coupling, following [13] one inserts the complete set of intermediate states with H and H∗ quantum numbers in (2.3) and employs the double dispersion relation for the amplitude F (q2, (p + q)2) in the two independent variables q2. At q2, (p + q) m2Q, the dispersion relation (2.6) is matched to the result of the QCD calculation of F (q2, (p + q)2) For the latter, we use the light-cone OPE in terms of pion. Following the general outline of QCD sum rule derivation [33], we employ the quark-hadron duality ansatz To this end, we will represent the OPE result for the correlation function in a form of double dispersion integral:. For the latter we will use the two-point QCD sum rules with the same NLO accuracy and the recent lattice QCD results
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