G. M. Zinovjev

Hot and dense gas of quark quasi-particles

Some features of hot and dense gas of quarks which are considered as the quasi-particles of the model Hamiltonian with four-fermion interaction are studied. Being adapted to the Nambu–Jona-Lasinio model this approach allows us to accommodate a phase transition similar to the nuclear liquid-gas one at the proper scale. It allows us to argue the existence of the mixed phase of vacuum and baryonic matter (even at zero temperature) as a plausible scenario of chiral symmetry (partial) restoration.

Some peculiarities in response to filling up the Fermi sphere with quarks

Considering quarks as the quasi-particles of the model Hamiltonian with four-fermion interaction we study response to the process of filling up the Fermi sphere with quarks, calculate the vacuum pressure and demonstrate the existence of filled-in state degenerate with the vacuum one.

Behavior of the gluon condensate in response to filling the Fermi sphere

The effect of the filling of the Fermi sphere with quarks of dynamically generated mass on the instanton liquid in a hot and dense strongly interacting medium is investigated. Among other things, it is shown that, in relation to the value characteristic of the Nambu-Jona-Lasinio model, the boundary of the phase transition restoring chiral invariance is shifted toward a greater chemical potential by about 100 MeV.

Diquark condensate and quark interaction with an instanton liquid

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 μc. This in turn induces a considerable growth of the threshold quark-matter density at which one expects the emergence of color superconductivity.

Correlation effects and bound states

Bound states in a simple quark model that are due to correlation effects are analyzed. The confining properties of this model in meson (quark-antiquark and diquark) channels manifest themselves at any quark momenta, and an extra potential field may only enhance the confining effect.

Some special features in the filling of the Fermi sphere with quark quasiparticles

The filling of the Fermi sphere with quarks treated as quasiparticles of the model Hamiltonian for four-fermion interaction is studied.

Phase structure of quark systems in models with four-fermion interaction

The features of a hot and dense gas of quarks that are considered as quasiparticles of a model Hamiltonian with four-fermion interaction are studied. Adapted to the Nambu-Jona-Lasinio model, this approach allows us to accommodate a phase transition similar to the nuclear liquid-gas one. Arguments are given in favor of the statement that a plausible scenario of (partial) chiral-symmetry restoration (even at zero temperature) in such a system could be a mixed phase of the vacuum and normal baryonic matter. The properties of the transition layer separating the two media in question are also discussed.

Sigma meson and phonon-like excitations of the instanton vacuum

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.

Screening of a color field in an instanton liquid

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.

Spectrum of heavy quarkonia in an instanton medium

The energy-level shift in heavy-quarkonium systems that is caused by fluctuations of vacuum gluon fields is estimated by simulating these fields by an instanton liquid. The use of the corresponding vacuum correlation function makes it possible to go beyond the dipole approximation. The width of energy levels with respect to decay to e+e− pairs is also given. It is shown that, both for bottomonium and for charmonium systems, an instanton medium can ensure a scale of shifts and widths of levels that is compatible with experimental data. In particular, it is indicated that a sizable logarithmic contribution at short distances is peculiar to the instanton vacuum.