arXiv subjects

Yu. A. Simonov

Publications and source records attributed to Yu. A. Simonov.

At least 181 records · Page 10Linked to original sources

arXiv2001

QCD string in light-light and heavy-light mesons

The spectra of light-light and heavy-light mesons are calculated within the framework of the QCD string model, which is derived from QCD in the Wilson loop approach. Special attention is payed to the proper string dynamics that allows us to reproduce the straight-line Regge trajectories with the inverse slope being 2πσfor light-light and twice as small for heavy-light mesons. We use the model of the rotating QCD string with quarks at the ends to calculate the masses of several light-light mesons lying on the lowest Regge trajectories and compare them with the experimental data as well as with the predictions of other models. The masses of several low-lying orbitally and radially excited heavy--light states in the D, D_s, B, and B_s meson spectra are calculated in the einbein (auxiliary) field approach, which has proven to be rather accurate in various calculations for relativistic systems. The results for the spectra are compared with the experimental and recent lattice data. It is demonstrated that an account of the proper string dynamics encoded in the so-called string correction to the interquark interaction leads to an extra negative contribution to the masses of orbitally excited states that resolves the problem of the identification of the D(2637) state recently claimed by the DELPHI Collaboration. For the heavy-light system we extract the constants \barΛ, λ_1, and λ_2 used in Heavy Quark Effective Theory (HQET) and find good agreement with the results of other approaches.

hep-ph↗

arXiv2001

Finite temperature correlation functions

Lattice measurements of the Pisa group (A.Di Giacomo et al., hep-lat/9603018) are analyzed numerically and parameters of correlation functions are extracted from the data - both below and above deconfinement temperature Tc. Gluon condensate is found for six temperatures in the interval 0.956 Tc - 1.131 Tc and field distributions in deconfined phase are obtained.

hep-ph↗

arXiv2000

Analytic Methods in Nonperturbative QCD

Recently developed analytic methods in the framework of the Field Correlator Method are reviewed in this series of four lectures and results of calculations are compared to lattice data and experiment. Recent lattice data demonstrating the Casimir scaling of static quark interaction strongly support the FCM and leave very little space for all other theoretical models, e.g. instanton gas/liquid model. Results of calculations for mesons, baryons, quark-gluon plasma and phase transition temperature demonstrate that new analytic methods are a powerful tool of nonperturbative QCD along with lattice simulations.

hep-ph↗

arXiv2000

QCD string in mesons and baryons

Field distributions generated by static quark-antiquark and QQQ sources are calculated analytically in the framework of Gaussian (bilocal) approximation of Field Correlator Method (FCM). Special attention is paid to the QQQ system and asymmetric configurations are also studied. In both quark-antiquark and QQQ cases the string consists mainly of longitudinal color electric field. Transverse color electric field contribution is shown to be less then 3%. Baryon string has an Y-like shape with a deep well at the string junction position. Field distributions for quark-diquark and for three quarks on one line are considered. The interaction potential for quarks forming an equilateral triangle is calculated. The material of the paper is illustrated by 24 3D colored pictures.

hep-ph↗

arXiv2000

Field distributions in heavy mesons and baryons

Field distributions generated by static quark-antiquark and QQQ sources are calculated analytically in the framework of the Field Correlator Method (FCM) using Gaussian (bilocal) correlator. In both cases the string consists mostly of longitudinal color electric field, while transverse electric field contributes locally less then 3%, in agreement with earlier lattice studies. In the QQQ case the profile of the Y shape was calculated for the first time and found to have a complicated structure with a deep well at the string junction position. Possible consequences of this form for the baryon structure are discussed.

hep-ph↗

arXiv2000

Magnetic string contribution to hadron dynamics in QCD

Dynamics of a light quark in the field of static source (heavy-light meson) is studied using the nonlinear Dirac equation, derived recently. Special attention is paid to the contribution of magnetic correlators and it is found that it yields a significant increase of string tension at intermediate distances. The spectrum of heavy-light mesons is computed with account of this contribution and compared to experimental and lattice data.

hep-ph↗

arXiv2000

Gluelump spectrum in the QCD string model

Spectrum of gluons in the adjoint source field is computed analytically using the QCD string Hamiltonian, containing only one parameter - string tension, fixed by meson and glueball spectrum. Spin splitting is shown to be small. A good agreement is observed with spatially generated gluelump states measured on the lattice. Important role of gluelumps defining the behaviour of field-strength correlators is stressed and correspondence with earlier computations of the latter is established.

hep-ph↗

arXiv2000

Baryon magnetic moments in the QCD string approach

Magnetic moments of baryons composed of light and strange quarks are computed for the first time through the only parameter of the model -- string tension $σ$. Resulting theoretical values differ from the experimental ones typically by about 10%.

hep-ph↗

arXiv2000

Glueball masses and Pomeron trajectory in nonperturbative QCD

Using a nonperturbative method based on asymptotic behaviour of Wilson loops we calculate masses of glueballs and corresponding Regge-trajectories. The method contains no fitting parameters and the mass scale is fixed by the meson Regge slope. Theoretical predictions for lowest glueball states are in a perfect agreement with lattice results. The leading glueball trajectory and its relation to the Pomeron is discussed in details. Important role of mixing between glueball and q\bar q trajectories is emphasized.

hep-ph↗

arXiv2000

QCD and Theory of Hadrons

Nonperturbative QCD approach is systematically derived starting from the QCD Lagrangian. Treating spin effects as a perturbation, one obtains the universal effective Hamiltonian describing mesons, hybrids and glueballs. Constituent mass of quark and gluon is calculated via string tension. The resulting spectrum of mesons, hybrids and glueballs obtained is in good overall agreement with lattice data and experiment.

hep-ph↗

arXiv2000

Casimir scaling as a test of QCD vacuum

Recent accurate measurements of static potentials between sources in various representations of the gauge group SU(3) performed by G.Bali provide a crucial test of the QCD vacuum models and different approaches to confinement. The Casimir scaling of the potential observed for all measured distances implies strong suppression of higher cumulant contributions. The consequences for the instanton vacuum model and the spectrum of the QCD string are also discussed.

hep-ph↗

arXiv2000

Test of the QCD vacuum with the sources in higher representations

Recent accurate measurement by G.Bali of static potentials between sources in various SU(3) representations provides a crucial test of the QCD vacuum and of different theoretical approaches to the confinement. In particular, the Casimir scaling of static potentials found for all measured distances implies a strong suppression of higher cumulants and a high accuracy of the Gaussian stochastic vacuum. Most popular models are in conflict with these measurements.

hep-ph↗

arXiv2000

String formation and chiral symmetry breaking in the heavy-light quark-antiquark system in QCD

The effective quark Lagrangian is written for a light quark in the field of a static antiquark, explicitly containing field correlators as coefficient functions of products of quark operators. At large N_c the closed system of equations for the gauge-invariant quark Green's function in the field of static source is examined analytically. The formation of the string connecting the light quark to the static source is observed numerically. The scalar Lorentz nature of the resulting confinement is shown to hold for the considered case, implying chiral symmetry breaking. The resulting spectrum with and without perturbative gluon exchanges is obtained numerically and compared to the B and D meson masses and HQET.

hep-ph↗

arXiv1999

Dynamical equations for mesons and baryons in large N_c QCD

New equations are derived for meson and baryon Green's functions in a systematic method using the QCD Lagrangian and large N_c approximation as a starting point. The equations are shown to contain both confinement dynamics and chiral symmetry breaking. Linear Regge trajectories are demonstrated for the solutions.

hep-ph↗

arXiv1999

Glueball spectrum and the Pomeron in the Wilson loop approach

Using a nonperturbative method based on asymptotic behaviour of Wilson loops we calculate masses of glueballs and corresponding Regge-trajectories. The only input is string tension fixed by meson Regge slope, while perturbative contributions to spin splittings are defined by standard alpha_s values. The masses of lowest glueball states are in a perfect agreement with lattice results. The leading glueball trajectory which is associated with Pomeron is discussed in details and its mixing with f and f' trajectories is taken into account.

hep-ph↗

arXiv1999

Rotating QCD string and the meson spectrum

The spectra of light-light and heavy-light mesons are described by spinless Salpeter equation and Dirac equation respectively, which predict linear dependence of the meson mass squared M^2 on angular momentum J and number of radial nodes n. Both spectra are computed by the WKB method and shown to agree with exact numerical data within few percent even for the lowest levels. The drawback of Salpeter and Dirac equation is that (inverse) Regge slopes do not coincide with the string ones, 2πσand πσrespectively, because the string dynamics is not taken into account properly. The lacking string rotation is introduced via effective Hamiltonian derived from QCD which generates linear Regge trajectories for light mesons with the correct string slope.

hep-ph↗

arXiv1999

High-momentum asymptotics from the Fock-Feynman- Schwinger path integral

The asymptotics of n-point Green's function at large external momenta is obtained in the exponentiated form using the Fock-Feynman-Schwinger representation for propagators in the external field. The method is applied to gauge theories such as QCD and QED, and the Sudakov form-factor is calculated as an example in QED and meson form-factor in QCD. Nonperturbative contributions can be conveniently included, as it is demonstrated in the example of the confinement correction to the form-factor.

hep-ph↗

arXiv1999

Perturbative-nonperturbative interference in the static QCD interaction at small distances

Short distance static quark--antiquark interaction is studied systematically using the background perturbation theory with nonperturbative background described by field correlators. A universal linear term $\frac{6N_cα_sσr}{2π}$ is observed at small distance $r$ due to the interference between perturbative and nonperturbative contributions. Possible modifications of this term due to additional subleading terms are discussed and implications for systematic corrections to OPE are formulated.

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