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We study quark behavior in a strong stochastic gluon field. Based on the procedure of the averaged description, we derive the effective Hamiltonian and find its ground state in the Hartree-Fock-Bogoliubov approximation. We compare different model Hamiltonians. We discuss the chiral limit transition in detail in the example of the Keldysh model. [ABSTRACT FROM AUTHOR]

The origin of the lightest scalar mesons is studied in the framework of the instanton liquid model of the QCD vacuum. The impact of phonon-like vacuum excitations on the σ-meson features is qualitatively analyzed. In particular, it is noticed that the changes produced in the scalar sector may unexpectedly become quite considerable in spite of insignificant values of corrections to the dynamical quark masses and then the medley of σ-meson and those excitations may reveal itself as broad resonance states of different masses. [ABSTRACT FROM AUTHOR]

The possible nature of two experimentally observed scalar mesons that are widely spaced in mass and whose special features may be caused by the excitations of the instanton liquid considered as a model of the QCD vacuum. It is shown that mass changes in the scalar sector may prove to be unexpectably large, even though the scale of such corrections to the dynamical quark mass is relatively small. [ABSTRACT FROM AUTHOR]

The screening of an external color field in an instanton liquid is studied. Effective Lagrangians are derived for a weak field and for a strong field in the long-wave approximation. The coupling-constant dependence of the feedback of the field on the instanton liquid is estimated by considering the model problem of a Euclidean pointlike charged color source. [ABSTRACT FROM AUTHOR]

We consider the behavior of an (anti)instanton in the field of a pointlike source of a Euclidean non-Abelian field and investigate (anti)instanton deformations described by variations of its characteristic parameters. We formulate the variational problem of seeking the corresponding “crumpled” topological configurations and solve it algebraically using the Ritz method (of multipole decomposition of deformation fields). We investigate the domain of parameters specific for the instanton liquid model. We propose a simple method of taking contributions of such configurations in the functional integral into account approximately. In the framework of superposition analysis, we obtain an estimate for the mean energy of the source in the instanton liquid, and the estimate increases linearly with distance. In the case of a dipole in the color-singlet state, the energy is a linear function of the distance between the sources with the “strength” coefficient agreeing well with the known model and lattice estimates. [ABSTRACT FROM AUTHOR]

The interaction of light quarks with an instanton liquid is considered at nonzero density of quark/baryon matter in a phase where the diquark condensate is nonzero. It is shown that the inclusion of the relevant perturbation of the instanton liquid leads to an increase in the quark chemical potential µ[sub c]. This in turn induces a considerable growth of the threshold quark-matter density at which one expects the emergence of color superconductivity. [ABSTRACT FROM AUTHOR]

For the case of finite quark and baryon densities, the interaction of light quarks with an instanton liquid is considered in a phase that involves a nonvanishing chiral condensate. The generating functional is considered in the tadpole approximation, and the behavior of the dynamical quark mass and the behavior of the chiral condensate, as well as the behavior of the instanton-liquid (gluon-condensate) density, which grows slightly with the quark chemical potential, are explored. Arguments are presented in favor of the statement that the quark-density threshold for the emergence of a diquark condensate grows sizably owing to interaction with the instanton liquid. [ABSTRACT FROM AUTHOR]

The effect of quarks on an instanton liquid through the excitation of adiabatic phonon-like modes in it is considered. An effective Lagrangian that includes a scalar color-singlet field interacting with quarks is derived, and the relevant generating functional is estimated in the tadpole approximation. The nature of this dynamical field as a mediator of interaction at soft momenta and its possible relationship with unusual properties of the sigma meson are discussed. [ABSTRACT FROM AUTHOR]

Phonon-like excitations of an anti-instanton-instanton liquid that are due to adiabatic variations in the instanton dimension are considered on the basis of an approximate calculation of the relevant path integral, which is saturated by quasizero modes. The kinetic term and the effective Lagrangian are found for such excitations. The properties of their spectrum, which has a mass gap determined by Λ[sub QCD], are discussed. [ABSTRACT FROM AUTHOR]