Searcharxiv⌕ Search

arXiv subjects

Yu. A. Simonov

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

At least 145 records · Page 8Linked to original sources
arXiv2004

Dynamics of confined gluons

Propagation of gluons in the confining vacuum is studied in the framework of the background perturbation theory, where nonperturbative background contains confining correlators. Two settings of the problem are considered. In the first the confined gluon is evolving in time together with static quark and antiquark forming the one-gluon static hybrid. The hybrid spectrum is calculated in terms of string tension and is in agreement with earlier analytic and lattice calculations. In the second setting the confined gluon is exchanged between quarks and the gluon Green's function is calculated, giving rise to the Coulomb potential modified at large distances. The resulting screening radius of 0.5 fm presents a serious problem when confronting with lattice and experimental data. A possible solution of this discrepancy is discussed.

hep-ph↗
arXiv2004

The coupled-channel analysis of the D and D_s mesons

The shift of the p-wave $D_s$ meson mass due to coupling to the DK channel is calculated without fitting parameters using the chiral Lagrangian. As a result the original $Q\bar q$ mass 2.490 MeV generically calculated in the relativistic quark models is shifted down to the experimental value 2317 MeV. With the same Lagrangian the shift of the radial excited $1^-$ level is much smaller, while the total width $Γ> 100$ MeV and the width ratio is in contradiction with the $D^*(2632)$ state observed by SELEX group.

hep-ph↗
arXiv2004

RG solutions for α_s at large N_c in d=3+1 QCD

Solutions of RG equations for $β(α)$ and $α(Q)$ are found in the class of meromorphic functions satisfying asymptotic conditions at large $Q$ (resp. small $α)$, and analyticity properties in the $Q^2$ plane. The resulting $α_R(Q)$ is finite in the Euclidean $Q^2$ region and agrees well at $Q\geq 1$ GeV with the $\bar{MS} α_s(Q)$.

hep-ph↗
arXiv2004

Chiral Symmetry Breaking in QCD

Chiral Symmetry Breaking (CSB) is derived in QCD starting from the QCD Lagrangian and using Field Correlators Method (FCM). The kernel in the resulting equations responsible for CSB is directly connected to confinement, and therefore both phenomena occur and vanish together as supported by lattice data. Chiral Lagrangian and quark-meson Lagrangian are derived with explicit coefficients and compared to standard expressions. Spectrum of Nambu-Goldstone mesons and their radial excitations is calculated in good agreement with experiment.

hep-ph↗
arXiv2004

The matrix Hamiltonian for hadrons and the role of negative-energy components

The world-line (Fock-Feynman-Schwinger) representation is used for quarks in arbitrary (vacuum and valence gluon) field to construct the relativistic Hamiltonian. After averaging the Green's function of the white $q\bar q$ system over gluon fields one obtains the relativistic Hamiltonian, which is matrix in spin indices and contains both positive and negative quark energies. The role of the latter is studied in the example of the heavy-light meson and the standard einbein technic is extended to the case of the matrix Hamiltonian. Comparison with the Dirac equation shows a good agreement of the results. For arbitrary $q\bar q $ system the nondiagonal matrix Hamiltonian components are calculated through hyperfine interaction terms. A general discussion of the role of negative energy components is given in conclusion.

hep-ph↗
arXiv2004

Current correlators in QCD: OPE versus large distance dynamics

We analyse the structure of current-current correlators in coordinate space in large $N_c$ limit when the corresponding spectral density takes the form of an infinite sum over hadron poles. The latter are computed in the QCD string model with quarks at the ends, including the lowest states, for all channels. The corresponding correlators demonstrate reasonable qualitative agreement with the lattice data without any additional fits. Different issues concerning the structure of the short distance OPE are discussed.

hep-ph↗
arXiv2004

The quark-gluon Mixed Condensate calculated via Field Correlators

The quark-gluon mixed condensate $g<\bar q σ_{μν} F_{μν} q>$ is calculated in the Gaussian approximation of the Field Correlator Method. In the large N_c limit and for zero mass quarks one obtains a simple result, $m^2_0 \equiv \frac{g<\bar q σ_{μν} F_{μν} q>}{<\bar q q>} = \frac{16σ}π$, where $σ$ is the string tension. For a standard value $σ=0.18 GeV^2$ one obtains $m^2_0=1 GeV^2$ in good agreement with the QCD sum rules estimate $m^2_0 = (0.8\pm 0.2) GeV^2$ and the latest lattice result $m^2_0 \cong 1 GeV^2$.

hep-ph↗
arXiv2004

Regge Behavior of DIS Structure Functions

Building on previous works of the mid 1960's, we construct an integral equation for forward elastic scattering (t=0) at arbitrary virtuality Q^2 and large s=W^2. This equation sums the ladder production of massless intermediate bosons to all orders, and the solution exhibits Regge behavior. The equation is used to study scattering in a simple chi^2 phi scalar theory, where it is solved appoximately and applied to the study of DIS at small x. We find that the model can naturally describe the quark distribution in both the large x region and the small x region dominated by Reggeon exchange.

nucl-th↗
arXiv2003

Pentaquark spectrum in string dynamics

The masses of $uudd\bar s $ and $uudd\bar d$ pentaquarks are evaluated in a framework of the Effective Hamiltonian approach to QCD using the Jaffe-Wilczek $[ud]^2\bar q$ approximation. The mass of the $[ud]^2\bar s$ state is found to be $\sim 300-500$ MeV higher than the observed $Θ^+(1540)$ mass.

hep-ph↗
arXiv2003

The QCD vacuum, confinement and strings in the Vacuum Correlator Method

In this review paper the QCD vacuum properties and the structure of color fields in hadrons are studied using the complete set of gauge-invariant correlators of gluon fields. Confinement in QCD is produced by the correlators of some certain Lorentz structure, which violate abelian Bianchi identities and therefore are absent in the case of QED. These correlators are used to define an effective colorless field, which satisfies Maxwell equation with nonzero effective magnetic current. With the help of the effective field and correlators it is shown that quarks are confined due to effective magnetic currents, squeezing gluonic fields into a string, in agreement with the ``dual Meissner effect''. Distribution of effective gluonic fields are plotted in mesons, baryons and glueballs with static sources.

hep-ph↗
arXiv2003

QCD: Confinement, Hadron Structure and DIS

The main features of QCD, e.g. confinement, chiral symmetry breaking, Regge trajectories are naturally and economically explained in the framework of the Field Correlator Method (FCM). The same method correctly predicts the spectrum of hybrids and glueballs. When applied to DIS and high-energy scattering it leads to the important role of higher Fock components in the Fock tower of moving hadron, containing primarily gluonic excitations.

hep-ph↗
arXiv2003

Nonperturbative quark dynamics in a baryon

Field-correlator method is used to calculate nonperturbative dynamics of quarks in a baryon. General expression for the 3q Green's function is obtained using Fock-Feynman-Schwinger (world-line) path integral formalism, where all dynamics is contained in the 3q Wilson loop with spin-field insertions. Using lowest cumulant contribution for Wilson loop one obtains an Y-shaped string with a deep hole at the string junction position. Using einbein formalism for the quark kinetic terms one automatically obtains constituent quark masses, calculable through the string tension. Resulting effective action for 3q plus Y-shaped strings is quantized in the path-integral formalism to produce two versions of Hamiltonian,one -in the c.m. and another in the light-cone system. Hyperspherical formalism is used to calculate masses and wave functions. Simple estimates in lowest approximation yield baryon masses in good agreement with experiment without fitting parameters.

hep-ph↗
arXiv2003

Pseudoscalar mesons and their radial excitations from the Effective Chiral Lagrangian

Effective Chiral Lagrangian is derived from QCD in the framework of Field Correlator Method. It contains the effects of both confinement and chiral symmetry breaking due to a special structure of the resulting quark mass operator. It is shown that this Lagrangian describes light pseudoscalar mesons, and Gell-Mann-Oakes-Renner relations for pions, eta and K mesons are reproduced. Spectrum of radial excitations of pions and K mesons is found and compared to experimentally known masses.

hep-ph↗
arXiv2003

Resolution of the pion puzzle: the QCD string in Nambu-Goldstone mesons

Pions and kaons have double nature: the chiral dynamics of Nambu-Goldstone bosons together with the usual string dynamics common to all mesons. To uncover the interplay of both dynamics the effective chiral Lagrangian is derived from the QCD Lagrangian using the Field Correlator Method and the pion self-energy (mass) operator is written explicitly. The latter contains an infinite number of poles, but normalized to zero at zero momentum because of spontaneous chiral symmetry breaking. As a result one obtains the Gell-Mann-Oakes-Renner relation for the ground state pion and (slightly shifted by chiral dynamics) the usual spectrum of radially excited pions starting with $π(1300)$.

hep-ph↗
arXiv2003

New spectral representation and evaluation of f_πand the quark condensate <\bar q q> in the terms of string tension

New spectral representations for f_πand chiral condensate are derived in QCD and used for calculations in the large N_c limit. Both quantities are expressed in this limit through string tension σand gluon correlation length T_g without fitting parameters. As a result one obtains <\bar q q> = - N_cσ^2 T_g a_1, f_π=\sqrt{N_c} σT_g a_2, with a_1=0.0823, a_2=0.30. Taking σ=0.18 GeV^2 and T_g=1 GeV^(-1), as known from analytic and lattice calculations, this yields <\bar q q>(μ=2 GeV)=-(0.225 GeV)^3, f_π=0.094 GeV, which is close to the standard values.

hep-ph↗
arXiv2003

The QCD spectrum: mixing, strong decays and the role of sea quarks

The light hadron spectrum as computed in nonperturbative QCD is reviewed and compared to lattice data and experiment. The mixing of mesons, hybrids and glueballs is calculated in the Field Correlator Method. The strong decay mechanisms are found out in the method and compared to the known phenomenological models. The role of sea quarks (unquenched approximation) is studied analytically using radially excited mesons as an example, and compared to experiment.

hep-ph↗
arXiv2003

Triangular and Y-shaped hadrons with static sources

The structure of hadrons consisting of three static color sources in fundamental (baryons) or adjoint (three-gluon glueballs) representations is studied. The static potentials of glueballs as well as gluon field distributions in glueballs and baryons are calculated in the framework of field correlator method.

hep-ph↗