arXiv subjects

S. V. Mikhailov

Publications and source records attributed to S. V. Mikhailov.

78 records · Page 5Linked to original sources

arXiv1997

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 $λ_q^2$ and gluons $λ_g^2$ in the QCD vacuum and obtain parameterless predictions for the ratio $λ_g^2/λ_q^2 = 12/5$, and for some ratios of different vacuum condensates of higher dimensions. The nonlocal properties of quark and gluon condensates are analyzed, and insufficiency of the single instanton approximation is discussed.

hep-ph↗

arXiv1997

QCD Sum Rules For Pion Wave Function Revisited

We analyze new QCD sum rules for the pion wave function $ϕ_π(x)$, obtained recently by A.V. Radyushkin in the framework of the non-local vacuum condensates method for non-diagonal correlators, and suggest a new approach for extracting wave functions of the $π$-meson and of its first resonances. As a result we obtain approximately the same form of the pion wave function by using two different methods and for two different ansatzes of non-local quark condensates. We predict the mass of the $π'$-resonance and obtain the form of its wave function. The first method uses integrated (in a sense) properties of ansatzes and may be considered as an alternative to traditional borel SR.

hep-ph↗

arXiv1997

Integral Transform Technique for Meson Wave Functions

In a recent paper [1] we have proposed a new approach for extracting the wave function of the $π$-meson $φ_π(x)$ and the masses and wave functions of its first resonances from the new QCD sum rules for non-diagonal correlators obtained in [2]. Here, we test our approach using an exactly solvable toy model as an illustrating example. We demonstrate the validity of the method and suggest a pure algebraic procedure for extracting the masses and wave functions relating to the case under investigation. We also explore the stability of the procedure under perturbations of the theoretical part of the sum rule. In application to the pion case, this results not only in the mass and wave function of the first resonance ($π'$), but also in the estimation of $π''$-mass.

hep-ph↗

arXiv1996

Continuous mass-dependent analysis of the non--singlet DIS data

We consider the issue of an accurate description of the evolution of the non-singlet structure function moments $M_n(Q)$ near heavy quark threshold. To this aim we propose a simple modification of the standard massless \MSbar scheme approach to the next-to-leading QCD analysis of DIS data. We apply it to the processing of the modern CCFR data for $xF_3$ structure function and extract the value of $α_s(M_z) \approx 0.108 \pm 0.004$ We check also the consistency of light gluino hypothesis with CCFR data.

hep-ph↗

arXiv1994

The Photon Structure Function $F_2$ in QCD with Nonlocal Vacuum Quark Condensates

We calculate the contribution from nonlocal vacuum condensates of quark fields to the hadronic part of the photon structure function $F_2(x)$ in the operator product expansion approach to QCD. The result is a smooth function of $x$ and its magnitude is comparable with one of gluon condensate. Extrapolation to the case of real photon is realized with the help of the model, suggested by Gorsky et al. As a result we obtain a substantial improvement of the agreement with experimental data for the standard value of the parameter $λ_q^2 \equiv \langle\bar qD^2 q\rangle /\langle\bar qq\rangle \approx 0.5 \ \ GeV^2 $.}

hep-ph↗

arXiv1994

Mass Dependent $α_S$ Evolution and the Light Gluino Existence

There is an intriguing discrepancy between α_s(M_Z) values measured directly at the CERN $Z_0$-factory and low-energy (at few GeV) measurements transformed to $Q=M_{Z_0}$ by a massless QCD α_s(Q) evolution relation. There exists an attempt to reconcile this discrepancy by introducing a light gluino $\gl$ in the MSSM. We study in detail the influence of heavy thresholds on α_s(Q) evolution. First, we consruct the "exact" explicit solution to the mass-dependent two-loop RG equation for the running α_s(Q). This solution describes heavy thresholds smoothly. Second, we use this solution to recalculate anew α_s(M_Z) values corresponding to "low-energy" input data. Our analysis demonstrates that using {\it mass-dependent RG procedure} generally produces corrections of two types: Asymptotic correction due to effective shift of threshold position; Local threshold correction only for the case when input experiment lies in the close vicinity of heavy particle threshold: $Q_{expt} \simeq M_h $. Both effects result in the effective shift of the \asmz values of the order of $10^{-3}$. However, the second one could be enhanced when the gluino mass is close to a heavy quark mass. For such a case the sum effect could be important for the discussion of the light gluino existence as it further changes the $\gl$ mass.

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