arXiv subjects
Publications and source records attributed to A. V. Pimikov.
We discuss the end-point behavior of the pion distribution amplitude (DA) and calculate its slope using QCD sum rules with nonlocal condensates. This is done in terms of the standard derivative and also with the help of an "integral derivative", recently obtained by us. Our approach favors a value of the slope of the order (or less) of the asymptotic DA and is in clear disagreement with flat-type pion DAs.
Starting from the QCD sum rules with nonlocal condensates for the pion distribution amplitude, we derive another sum rule for its derivative and its "integral" derivatives---defined in this work. We use this new sum rule to analyze the fine details of the pion distribution amplitude in the endpoint region $x\sim 0$. The results for endpoint-suppressed and flat-top (or flat-like) pion distribution amplitudes are compared with those we obtained with differential sum rules by employing two different models for the distribution of vacuum-quark virtualities. We determine the range of values of the derivatives of the pion distribution amplitude and show that endpoint-suppressed distribution amplitudes lie within this range, while those with endpoint enhancement---flat-type or CZ-like---yield values outside this range.
We present results of a calculation of the electromagnetic pion form factor within the framework of QCD Sum Rules with nonlocal condensates, using a perturbative spectral density which includes $O(α_s)$ contributions.
We discuss the QCD sum-rule approach for the spacelike electromagnetic pion form factor in the $O(α_s)$ approximation. We show that the nonlocality of the condensates is a key point to include nonperturbative contributions to the pion form factor. We compare our results with the Local-Duality predictions and show that the continuum threshold $s_0(Q^2)$ parameter is highly underestimated in the Local-Duality approach at $Q^2\gtrsim 2$ GeV$^2$. Using our fit for this parameter, $s_0^\text{LD}(Q^2)$, and applying the fractional analytic perturbation theory, we estimate with an accuracy of the order of 1% the $O(α_s^2)$ contribution to the pion's form factor.
We review a nonlocal-condensate approach and its application in QCD sum rules for the spacelike electromagnetic pion form factor. It is shown that the nonlocality of the condensates is a key point to include nonperturbative contributions to the pion form factor.
We present a detailed investigation of the spacelike pion's electromagnetic form factor using three-point QCD sum rules that exclusively involve nonlocal condensates. Our main methodological tools are a spectral density which includes $O(α_s)$ corrections, a suitably improved Gaussian ansatz to model the distribution of the average momentum of quarks in the QCD vacuum, and a perturbative scheme that avoids Landau singularities. Using this framework, we obtain predictions for the pion form factor together with error estimates originating from intrinsic theoretical uncertainties owing to the perturbative expansion and the nonperturbative method applied. We also discuss our results in comparison with other calculations, in particular, with those following from the AdS/QCD correspondence. We find good agreement of our predictions with measurements in the range of momenta covered by the existing experimental data between 1-10 GeV$^2$.
We present results of a calculation of the electromagnetic pion form factor within a framework of QCD Sum Rules with nonlocal condensates and using a perturbative spectral density which includes \mathcal{O}(α_s) contributions.
We investigate magnetic susceptibility and the leading twist light-cone distribution amplitude for the real photon in the framework of the nonlocal condensate approach at LO accuracy of perturbative expansion.
We describe the present status of the pion distribution amplitude (DA) as it originates from several sources: (i) a nonperturbative approach based on QCD sum rules with nonlocal condensates, (ii) an $O(α_s)$ QCD analysis of the CLEO data on F^{γγ^*π}(Q^2) with asymptotic and renormalon models for higher twists, and (iii) recent high-precision lattice QCD calculations of the second moment of the pion DA. We show predictions for the pion electromagnetic form factor, obtained in analytic QCD perturbation theory, and compare it with the JLab data on F_π(Q^2). We also discuss in this context an improved model for nonlocal condensates in QCD and show its consequences for the pion DA and the γγ^*\toπtransition form factor. We include a brief analysis of meson-induced massive lepton (muon) Drell--Yan production for the process π^{-}N\toμ^{+}μ^{-}X, considering both an unpolarized nucleon target and longitudinally polarized protons.
We describe the present status of the pion distribution amplitude as it originated from two sources: (i) a nonperturbative approach, based on QCD sum rules with nonlocal condensates and (ii) a NLO QCD analysis of the CLEO data on F^{γγ^*π}(Q^2), supplemented by the recent high-precision lattice calculations of the second moment of the pion distribution amplitude.
We show that the minimal Gaussian model of nonlocal vacuum quark and quark-gluon condensates in QCD generates the non-transversity of vector current correlators. We suggest the improved Gaussian model of the nonperturbative QCD vacuum, which respects QCD equations of motion and minimizes the revealed gauge-invariance breakdown. We obtain the refined values of pion distribution amplitude (DA) conformal moments using the improved QCD vacuum model and construct the allowed region for Gegenbauer coefficients a_2 and a_4 of the pion DA.