The chromo-dielectric model: Confinement,effective coupling and chiral invariance

The chromo-dielectric mechanism of absolute confinement is studied in the nontopological soliton model. The model lagrangian is chirally invariant, since it contains no direct coupling between the quarks and the scalar field. The static chromo-electric gluon propagator is calculated in medium in the one-loop approximation, and the ultraviolet divergence in the self-energy of fixed quarks is regulated by a form factor. Effective quark-scalar coupling emerges through the self-energy of the quarks in the dielectric medium, which is a function of the scalar field.     

Searching photon signal of quark-gluon plasma formation

The intensive radiation of magnetic bremsstrahlung type resulting from interaction of escaping quarks with the collective colour field ensuring the confinement and bringing back quarks into plasma is discussed as a new possible signal of quark-gluon plasma formation.     

Quark pair creation in color electric fields and effects of magnetic fields

The time evolution of a system where a uniform and classical SU(3) color electric field and quantum fields of quarks interact with each other is studied focusing on non-perturbative pair creation and its back reaction. We characterize a color direction of an electric field in a gauge invariant way, and investigate its dependence. Momentum distributions of created quarks show plasma oscillation as well as quantum effects such as the Pauli blocking and interference. Pressure of the system is also calculated, and we show that pair creation moderates degree of anisotropy of pressure. Furthermore, enhancement of pair creation and induction of chiral charge under a color magnetic field which is parallel to an electric field are discussed.     

Confinement model for quarks

A confinement model of hadron with its constituent quarks bound in a strong gravitational field is presented. The gravitational field plays the role of a medium having, as if, space dependent permeabilities from a fixed centre. The massless Dirac equation modified by the gravitational field is solved. The solution for the wavefunction of the quarks obtained shows the characteristic features of confinement, i.e., (i) wavefunction with higher energy states lying closer to the centre, (ii) equispaced energy levels without continuum, (iii) the quark orbits lying within a distance ∼ 10⁻¹⁴ cm, the characteristic radius of a typical hadron.     

QCD string in mesons and baryons

The distributions of fields generated by static $Q\bar Q$ and QQQ sources are calculated analytically within the bilocal approximation of the method of vacuum correlation functions. At large distances between the quarks, the fields assume a clear-cut stringlike shape. The main contribution to the string comes from the longitudinal component of the chromoelectric field. The contribution of the transverse chromoelectric field is below 3% of the contribution from the longitudinal component. A baryonic string has a Y-like shape with a deep well in the region of the string-junction position. Field distributions are considered for a quark-diquark configuration and in the case of three quarks occurring on a straight line. The interaction potential is calculated for three quarks residing at the vertices of an equilateral triangle.     

The Strong Interaction in Chromodynamics

L static classical solution of nonlinear gluon field belonging to the SU(3) octet representation is obtained which is inversely proportional to the couplicg constant g, and therefore cannot be obtained by usual perturbation method. The static field is used as the potential of the relativistic wave equation of quarks in hadron states. It is found that the motion of quarks and antiquarks in all kinds of hadrons including new particles Ψ, and γ can be described by simple harmonic oscillations with small corrections due to spin-dependen t interactions.     

Magnetic Effect Versus Thermal Effect on Quark Matter with a Running Coupling at Finite Densities

We investigate the quark matter in a strong magnetic field in the framework of SU(2) NJL model with a magnetic-field-dependent coupling. The spin polarization, the entropy per baryon, and the energy are studied by analyzing the competition of the magnetic effect and the thermal effect. The stronger magnetic field can enhance the spin polarization, arrange quarks in a uniform spin orientation, and change the energy per baryon drastically. However,it can hardly affect the entropy per baryon, which is dominated by the temperature. As the temperature increases, more quarks will be excited from the lowest Landau level up to higher Landau levels.     

Theories of quark confinement

It is conjectured that a non-Abelian gauge theory based on the color SU(3) group will confine quarks. Various techniques that have been applied to this question are reviewed. These include approximate methods based on strong coupling expansions of Hamiltonian and Euclidian lattice theories, instanton improvements on perturbation theory, and solutions of truncated Dyson-Schwinger equations for the gauge field propagator. Formal results based on electric-magnetic duality arguments and on the study of loop field theories are presented. Deconfinement at high temperatures, the inclusion of light quarks, and a possible reconciliation with a hypothetical discovery of free quarks are discussed.     

Cooper pairs? magnetic moment in MCFL color superconductivity

We investigate the effect of the alignment of the magnetic moments of Cooper pairs of charged quarks that form at high density in three-flavor quark matter. The high-density phase of this matter in the presence of a magnetic field is known to be the Magnetic Color-Flavor-Locked (MCFL) phase of color superconductivity. We derive the Fierz identities of the theory and show how the explicit breaking of the rotational symmetry by the uniform magnetic field opens new channels of interactions and allows the formation of a new diquark condensate. The new order parameter is a spin-1 condensate proportional to the component in the field direction of the average magnetic moment of the pairs of charged quarks. The magnitude of the spin-1 condensate becomes comparable to the larger of the two scalar gaps in the region of large fields. The existence of the spin-1 condensate is unavoidable, as in the presence of a magnetic field there is no solution of the gap equations with nonzero scalar gaps and zero magnetic moment condensate. This is consistent with the fact that the extra condensate does not break any symmetry that has not already been broken by the known MCFL gaps. The spin-1 condensate enhances the condensation energy of pairs formed by charged quarks and the magnetization of the system. We discuss the possible consequences of the new order parameter on the issue of the chromomagnetic instability that appears in color superconductivity at moderate density.     

Nonperturbative dynamics in the color-magnetic QCD vacuum

In the deconfinement phase of QCD, quarks and gluons interact with the dense stochastic color-magnetic vacuum. We consider the dynamics of quarks in this deconfinement phase using the field correlators method and derive an effective nonperturbative interquark potential, in addition to the usual perturbative short-range interaction. We find the resulting angular-momentum-dependent interaction to be attractive enough to maintain bound states and, for light quarks (and gluons), to cause emission of quark and gluon pairs. Possible consequences for the strong-interacting quark-gluon plasma are briefly discussed. The text was submitted by the authors in English.     

Pion condensation in a medium with massive quarks in the external chromomagnetic field

Pion condensation in a flavor-asymmetric quark medium with massive quarks in the external chromomagnetic field is considered. It is shown that the external field catalyzes pion condensation while the finite quark mass does not impede the onset of this phenomenon.     

Magnetic color-flavor locking phase in high-density QCD

We investigate the effects of an external magnetic field in the gap structure of a color superconductor with three massless quark flavors. Using an effective theory with four-fermion interactions, inspired by one-gluon exchange, we show that the long-range component B of the external magnetic field that penetrates the color-flavor locked phase modifies its gap structure, producing a new phase of lower symmetry. A main outcome of our study is that the B field tends to strengthen the gaps formed by Q-charged and Q-neutral quarks that coupled among themselves through tree-level vertices. These gaps are enhanced by the field-dependent density of states of the Q-charged quarks on the Fermi surface. Our considerations are relevant for the study of highly magnetized compact stars.     

The interquark potential: SU(2) colour gauge theory with fermions

Including dynamical fermions in the Monte Carlo simulation of the SU(2) gauge theory, the potential between static quarks is investigated on a 16×8³ lattice. The Coulomb part of the force is stronger as compared with the pure gauge field theory. At large distances indications are found for a deviation from the linear rise of the potential, expected from a break-up of the flux tube between the heavy quarks through spontaneous creation of light quark pairs.     

Quarks and glue: Equations of motion

The conceot of a linearly rising potential which serves to permanently binds quarks into hadrons is parlayed into field theoretic equations of motion for quarks and their accompanying glue fields. The usual fractionally charged are assumed to be comprised of degenerate color triplets. The gulons are assumed to be the naturally accompanying octet of color gauge fields which are needed to make color an exact gauge symmetry. Fourth derivatives of the gluon fields occur in the equations of motion in order that the gluons may transit the permanently binding force. The quark-glue coupling is not minimal, but is rather assumed to have a large anomalous spin coupling term. This produces large spin-spin forces between quarks, which apparently are required to account for the large percentage mass difference between the pion and the rho.     

Confinement of quarks in nonlocal quantum field theory

The model of quarks in the frame of nonlocal quantum field theory is demonstrated. Here all basic principles of quantum theory are conserved, quarks are automatically confined and the scaling behaviour of the amplitude of an inclusive process is manifested explicitly in lower orders of perturbation theory.On leave of absence from theDept. of Theoretical Physics, Comenius University, Bratislava, Czechoslovakia.     

ζ-Regularized Lagrangians for massive quarks in constant background mean-fields

Hawking's ζ-function regularization method is used in order to obtain the effective QCD Lagrangian for ordinary quarks moving in some constant background field. The general context is Adler's mean-field approximation to QCD, and an extension of his results is obtained for three particular models. Namely, at one loop order, massive quarks in a constant self-dual, pure colormagnetic, or pure colorelectric field are confined, and this is true for any number of quark flavors. Also, a criterion is established in order to calculate the values and signs of the imaginary parts for E- and B-fields. The final results for these imaginary parts are in agreement with those of Nielsen and Olesen and of Yildiz and Cox.     

Quark fragmentation in gauge theories

A theory of quark fragmentation is based on the phenomenon of spontaneous pair creation in a strong Coulomb field, applied to the color field surrounding the leading quarks.     

The Constituent Quark Exchange Model for the Bound State Nucleons

The aim of present article is to compare the different bound state parton distributions in the protons with those coming from the free protons experimental data and to investigate the effect of quark structure of protons on each other. So, the constituent quark model (CQM), in which the quarks are assumed to be the complex objects and was originally proposed by Altarelli et al. (ACMP), is used in the frame work of the quark exchange model (QEM) to calculate the parton distributions of bound protons. Unlike our previous works, the effect of sea quarks and gluons are included in the QEM. Our results are in agreement with those of Glück et al. (GRV) when we ignore the binding and the Fermi motion effects for the constituent quarks. In this case, we get more sea-quarks and gluons with respect to the bound state constituents quarks calculation. It is also shown that the QEM, which is a realistic formalism gives better result with respect to the Isgur and Karl et al. model which is a field theoretical approach. The ratio of the structure functions of neutron to proton is also calculated with the assumption of isospin symmetry and it is compared with the available data and our previous works.     

Dissociation of Quarkonium in a Strong Electric Field

The probability of tunnel decay of quarkonium (bond state of a heavy quark and a heavy antiquark) into free quarks in a strong electric field is estimated.