A. E. Dorokhov

Rare decay pi0 ---> e+ e-: Theory confronts KTeV data

Within the dispersive approach to the amplitude of the rare decay {pi}{sup 0}{yields}e{sup +}e{sup -} the nontrivial dynamics is contained only in the subtraction constant. We express this constant, in the leading order in (m{sub e}/{lambda}){sup 2} perturbative series, in terms of the inverse moment of the pion transition form factor given in symmetric kinematics. By using the CELLO and CLEO data on the pion transition form factor given in asymmetric kinematics, the lower bound of the decay branching ratio is found. The restrictions following from QCD allow us to make a quantitative prediction for the branching B({pi}{sup 0}{yields}e{sup +}e{sup -})=(6.2{+-}0.1){center_dot}10{sup -8} which is 3{sigma} below the recent KTeV measurement. We confirm our prediction by using the quark models and phenomenological approaches based on the vector meson dominance. The decays {eta}{yields}l{sup +}l{sup -} are also discussed.

Virtualities of Quarks and Gluons in QCD Vacuum and Nonlocal Condensates within Single Instanton Approximation

We calculate the lowest-dimensional nonlocal quark and gluon condensates within the single instanton approximation of the instanton liquid model. As a result, we determine the values of average virtualities of quarks {lambda}{sub q}{sup 2}{equivalent_to}{l_angle}:{bar q}D{sup 2}q:{r_angle}/{l_angle}:{bar q}q:{r_angle} and gluons {lambda}{sub g}{sup 2}{equivalent_to}{l_angle}:G{tilde D}{sup 2}G:{r_angle}/{l_angle}:GG:{r_angle} in the QCD vacuum and obtain parameterless predictions for the ratio {lambda}{sub g}{sup 2}/{lambda}{sub q}{sup 2}=12/5, and for some ratios of different vacuum condensates of higher dimensions. The nonlocal properties of quark and gluon condensates are analyzed, and the insufficiency of the single instanton approximation is discussed. {copyright} {ital 1997} {ital The American Physical Society}

PROTON SPIN WITHIN NONPERTURBATIVE QCD

A review of various approaches to the problem of the proton spin is presented. Arguments are given in favor of the idea that the answer to the “spin crisis” is to be found in fundamental nonperturbative properties of the QCD vacuum.

The pseudoscalar hadronic channel contribution of the light-by-light process to the muon (g−2) μ within the nonlocal chiral quark model

The light-by-light contribution to the anomalous magnetic moment of muon (g−2)μ from the hadronic exchanges in the neutral pseudoscalar meson channel is calculated in the nonlocal chiral quark model. The full kinematic dependence of the meson two-photon vertices from the virtualities of the mesons and photons is taken into account. It is demonstrated that the effect of the full kinematic dependence in the meson–photon vertices is to reduce the contribution of pseudoscalar exchanges comparing with the most of previous estimates and the result is

Pion pole light-by-light contribution to g-2 of the muon in a nonlocal chiral quark model

a_{\mu}^{\mathrm{PS,LbL}}=(5.85\pm0.87)\cdot10^{-10}

Adler function and hadronic contribution to the muon g - 2 in a nonlocal chiral quark model

. The status of various phenomenological and QCD short-distance constraints is discussed and the comparison with the predictions of other models is performed.

Gluon field strength correlation functions within a constrained instanton model

We calculate the pion-pole term of the light-by-light contribution to the g - 2 of the muon in the framework of an effective chiral quark model with instantonlike nonlocal quark-quark interaction. The full kinematic dependence of the pion-photon transition form factors is taken into account. The dependence of form factors on the pion virtuality decreases the result by about 15% in comparison to the calculation where this dependence is neglected. Further, it is demonstrated that the QCD constraints suggested by Melnikov and Vainshtein are satisfied within the model. The corresponding contributions originate from the box diagram as well from the pion-pole term. Our chiral nonlocal model result for the pion-pole light-by-light contribution to (g - 2)/2 of the muon is (6.3-6.7) × 10 -10 , which is in the ball park of other effective-model calculations.

Complete structure-dependent analysis of the decay P→l+l−

The behavior of the vector Adler function at spacelike momenta is studied in the framework of a covariant chiral quark model with instantonlike quark-quark interaction. This function describes the transition between the high-energy asymptotically free region of almost massless current quarks to the low-energy hadronized regime with massive constituent quarks. The model reproduces the Adler function and

\(VA\widetilde{V}\) correlator within the instanton vacuum model

V\ensuremath{-}A

QED radiative corrections to the decay pi^0 to e^+e^-

correlator extracted from the ALEPH and OPAL data on hadronic