We study the transition form factors of the light mesons in the kinematics, where one photon is real and other is virtual. Using the dispersive approach to axial anomaly we show that the axial anomaly in this case reveals itself as a collective effect of meson spectrum. This allows us to get the relation between possible corrections to continuum and to lower states within QCD method which does not rely on factorization hypothesis. We show, relying on the recent data of BaBar Collaboration, that the relative correction to continuum is quite small, and small correction to continuum can dramatically change the pion form factor.Comment: 12 pages, 3 figures, typos corrected, published in Phys. Lett.

The relation for transition form factors of and 0 is obtained by combining the exact nonperturbative QCD sum rule, following from the dispersive representation of axial anomaly, and quark-hadron duality. It is valid at all virtual photon momenta and allows one to express the transition form factors entirely in terms of meson decay constants. This relation is in a good agreement with experimental data.

The earlier introduced method of calculation of quark distributions in hadrons, based on QCD sum rules, is improved. The imaginary part of the virtual photon forward scattering amplitude on some hadronic current is considered in the case, when initial and final virtualities of the current p 2 1 , and p 2 2 are different, p 2 1 = p 2 2 . The operator product expansion (OPE) in p 2 1 , p 2 2 is performed. The sum rule for quark distribution is obtained using double dispersion representation of the amplitude on one side in terms of calculated in QCD OPE and on the other side in terms of physical states contributions. Double Borel transformation in p 2 1 , p 2 2 is applied to the sum rule, killing background non-diagonal transition terms, which deteriorated the accuracy in previous calculations. The case of valence quark distribution in pion is considered, which was impossible to treat by the previous method. OPE up to dimension 6 operators is performed and leading order perturbative corrections are accounted. Valence u-quark distribution in π + was found at intermediate x, 0.15 < x < 0.7 and normalization point Q 2 = 2 GeV 2 . These results may be used as input for evolution equations.

We consider the procedure of determination of induced quark condensates in the QCD sum rule approach. It is noted that the previous estimations of this value were very rough. It is shown, that the detailed analyses of this parameter of QCD vacuum leads to the conclusion that the value of the tensor susceptibility has opposite sign and much larger than estimations which were obtained before. The reason of this contradiction is discussed. It is noted that naive ways of determination of induced condensates may lead to wrong results. The case of tensor susceptibility is the example demonstrating the importance of the procedure which is applied for calculation of such condensates. New results for the nucleon tensor charge are presented. The tensor charge is related to the first moment of the transversity distribution function h 1 (x).

The part of the proton spin ⌺ carried by u,d,s quarks is calculated in the framework of the QCD sum rules in the external fields. The operators up to dimension 9 are accounted for. An important contribution comes from the operator of dimension 3, which in the limit of massless u,d,s quarks is equal to the derivative of the QCD topological susceptibility Ј(0). The comparison with the experimental data on ⌺ gives Ј(0)ϭ(2.3 Ϯ0.6)ϫ10 Ϫ3 GeV 2 . The limits on ⌺ and Ј(0) are found from self-consistency of the sum rule, ⌺տ0.05, Ј(0)տ1.6ϫ10 Ϫ3 GeV 2 . The values of g A ϭ1.37Ϯ0.10 and g A 8 ϭ0.65Ϯ0.15 are also determined.