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Couplings of heavy hadrons with soft pions from QCD sum rules

We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian from the QCD sum rules in an external axial field. We take into account the perturbative correction to the meson correlator in the infinite mass limit. With the perturbative correction and three successive power corrections, the meson correlator in an axial field becomes one of the best known correlators. In spite of this, the corresponding sum rule is not very stable. It yields the result g_1 F^2/(380MeV)^3 = 0.1 - 0.2, where F^2 = f_M^2 m/4 = (380MeV)^3 is the central value of the heavy meson decay constant with the perturbative correction. This result is surprisingly low as compared with the constituent quark model estimate g_1 = 0.75. The sum rules for g_{2,3} following from nondiagonal Sigma-Sigma and diagonal Lambda-Sigma baryon correlators in an external axial field suggest g_{2,3} = 0.4 - 0.7, while diagonal Sigma-Sigma and nondiagonal Lambda-Sigma baryon sum rules have too large uncertainties.