Color Dielectric Model Research Articles

NUCLEON IN NUCLEAR MEDIUM

The behavior of a nucleon in nuclear medium is discussed in Chiral Color Dielectric Model. It is assumed that the nucleons in nuclear medium produces a background dielectric field and the quark and dielectric field equations are solved self consistantly in presence of the dielectric field. A nucleon in nuclear medium is then constructed by means of standard procedure followed in chiral bag models. The corrections due to center of mass motion, color magnetic interaction and meson interaction are included. The calculations show that the nucleon becomes bigger in the medium but its mass does not change much. It is found that beyond a certian density, bound solutions in which quarks are bound in self-generated dielectric field are not possible. Thus, the calculations indicate that there is a critical density beyond which the matter consists of deconfined quarks.

The equation of state of dense matter: from nuclear collisions to neutron stars

The equation of state (EoS) of dense matter represents a central issue in the study of compact astrophysical objects and heavy ion reactions at intermediate and relativistic energies. We have derived a nuclear EoS with nucleons and hyperons within the Brueckner–Hartree–Fock approach, and joined it with quark matter EoS. For that, we have employed the MIT bag model, as well as the Nambu–Jona-Lasinio and the color dielectric models, and found that the NS maximum masses are not larger than 1.7 solar masses. A comparison with available data supports the idea that dense matter EoS should be soft at low density and quite stiff at high density.

ROTATING QUARK STAR IN CHIRAL COLOUR DIELECTRIC MODEL

The properties of rotating quark star are studied using the equation of state obtained from chiral colour dielectric model. The results are compared with those obtained from MIT bag model equation of state. The frequencies in the corotating innermost circular orbits for different central densities are evaluated and compared with the observed data.

Pentaquarks in chiral color dielectric model

Recent experiments indicate that a narrow baryonic state having strangeness +1 and mass of about 1540 MeV may be existing. Such a state was predicted in chiral model by Diakonovet al. In this work I compute the mass and width of this state in chiral color dielectric model. I show that the computed width is about 30 MeV. I find that the mass of the state can be fitted to the experimentally observed mass by invoking a color neutral vector field and its interaction with the quarks

The hadron-quark phase transition in neutron stars

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Hartree-Fock approach. For the quark sector, we employ the MIT bag model, as well as the Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and find that the NS maximum masses lie in the interval between 1.5 and 1.8 solar masses.

Hybrid stars with the color dielectric and the MIT bag models

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.7 solar masses, no matter the model chosen for describing the pure quark phase.

Dihyperons in chiral color dielectric model

The mass of the dibaryon having spin, parityJπ = 0+, isospinI = 0 and strangeness—2 is computed using chiral color dielectric model. The bare wave function is constructed as a product of two color-singlet three-quark clusters and then it is properly antisymmetrized by considering appropriate exchange operators for spin, flavor and color. Color magnetic energy due to gluon exchange, meson self energy and energy correction due to center of mass motion are computed. The calculation shows that the mass of the particle is 80 to 160 MeV less than twice λ mass.

Color dielectric model with two scalar fields

SU(2) Yang-Mills theory coupled in a non-minimal way to two scalar fields is discussed. For the massless scalar fields a family of finite energy solutions generated by an external, static electric charge is found. Additionally, there is a single solution which can be interpreted as confining one. Similar solutions have been obtained in the magnetic sector. In case of massive scalar fields the Coulomb problem is investigated. We find that asymptotic behavior of the fields can also, for some values of the parameter of the model, give confinement of the electric charge. Quite interesting one glueball--meson coupling gives the linear confining potential. Finally, it is shown that for one non-dynamical scalar field we derive the color dielectric generalization of the Pagels--Tomboulis model.

Stability of strange quark matter: MIT bag versus color dielectric model

We discuss the properties of strange matter, in particular the minimum of the energy per baryon number as a function of the strangeness fraction. We utilize both the MIT bag model and the color dielectric model and compare the energy per baryon with the masses of hyperons having the corresponding strangeness fraction, which are coherently calculated within both models. We also take into account the perturbative exchange of gluons. The results obtained in the two approaches allow to discuss the stability of strangelets. While the MIT bag model and the double minimum version of the color dielectric model allow the existence of strangelets, the single minimum version of the color dielectric model excludes this possibility.

Neutron Stars, Supernova Explosions and the Transition to Quark Matter

Abstract The structure of a hybrid star is discussed using both the MIT bag model and the Color Dielectric Model to describe the quark matter phase. A finite temperature equation of state is introduced to discuss the possibility that the transition to quark matter takes place during the pre-supernova collapse.

Neutron stars, supernova explosions and the transition to quark matter

The structure of a hybrid star is discussed using both the MIT bag model and the Color Dielectric Model to describe the quark matter phase. A finite temperature equation of state is introduced to discuss the possibility that the transition to quark matter takes place during the pre-supernova collapse.

Meson-baryon form factors in the chiral color dielectric model

The renormalized form factors for pseudoscalar meson-baryon coupling are computed in the chiral color dielectric model. This has been done by rearranging the Lippmann-Schwinger series for the meson-baryon scattering matrix so that it can be expressed as a baryon pole term with renormalized form factors and baryon masses and the rest of the terms which arise from the crossed diagrams. Thus we are able to obtain an integral equation for the renormalized meson-baryon form factors in terms of the bare form factors as well as an expression for the meson self-energy. This integral equation is solved, and renormalized meson baryon form factors and renormalized baryon masses are computed. The parameters of the model are adjusted to obtain a best fit to the physical baryon masses. The calculations show that the renormalized form factors are energy dependent and differ from the bare form factors primarily at momentum transfers smaller than 1 GeV. At nucleon mass, the change in the form factors is about 10% at zero momentum transfer. The computed form factors are soft with the equivalent monopole cutoff mass of about 500 MeV. The renormalized coupling constants are obtained by comparing the chiral color dielectric model interaction Hamiltonian with the standard form of the meson-nucleon interaction Hamiltonian. The ratio of $\ensuremath{\Delta}N\ensuremath{\pi}$ and $\mathrm{NN}\ensuremath{\pi}$ coupling constants is found to be about 2.15. This value is very close to the experimental value.

Hdibaryon in the chiral color dielectric model

The mass of the $H$ dibaryon with spin, parity ${J}^{\ensuremath{\pi}}{=0}^{+}$, and isospin $I=0$ is calculated in the framework of the chiral color dielectric model. The wave function of the $H$ dibaryon is expressed as a product of two color-singlet baryon clusters. Thus the quark wave functions within the cluster are antisymmetric. Appropriate operators are then used to antisymmetrize intercluster quark wave functions. The radial part of the quark wave functions are obtained by solving the quark and dielectric field equations of motion obtained in the color dielectric model. The mass of the $H$ dibaryon is computed by including the color magnetic energy as well as the energy due to meson interaction. The recoil correction to the $H$ dibaryon mass is incorporated by Peierls-Yoccoz technique. We find that the mass of the $H$ dibaryon is smaller than the $\ensuremath{\Lambda}\ensuremath{-}\ensuremath{\Lambda}$ threshold by over 100 MeV. The implications of our results on the present day relativistic heavy ion experiments are discussed.

Axial vector coupling constant in a chiral color dielectric model

The axial vector coupling constants of the \ensuremath{\beta} decay processes of the neutron and hyperon are calculated in SU(3) chiral color dielectric model (CCDM). Using these axial coupling constants of the neutron and hyperon, in the CCDM we calculate the integrals of the spin-dependent structure functions for the proton and neutron. Our result is similar to the results obtained by MIT bag and cloudy bag models (CBM).

PiN: Computation of pion-nucleon scattering and bound states with the color dielectric quark model

Described is a 9421 line Fortran program PiN that solves momentum-space integral Lippmann-Schwinger equations for the scattering observables and the bound/resonant state properties of the coupled ( πN, πΔ) system. The elementary interactions arise from the chiral color-dielectric quark and the cloudy bag models, which are computed by the code. The bound state wave functions of the quarks are computed by a separate code.

J/ ψ-dissociation by a color electric flux tube

We address the question of how a c — c̄state (a J/ ψ) can be dissociated by the strong color electric fields when moving through a color electric flux tube. The color electric flux tube and the dissociation of the heavy quarkonia state are both described within the Friedberg-Lee color dielectric model. We speculate on the importance of such an effect with respect to the observed J/ ψ-suppression in ultrarelativistic heavy ion collisions.

Recoil effects on nucleon electromagnetic form factors

The electromagnetic form factors are computed using eigenstates of linear momentum for the nucleon. The latter is described in the framework of the chiral color-dielectric model, projecting the hedgehog ansatz on eigenstates of angular momentum and isospin. Form factors are well reproduced, with the exception of the magnetic one for the proton, up to q 2 ⋍ 0.5 GeV 2 . The effect of the removal of the spurious center-of-mass contributions shows up mainly in the electric form factor of the proton. A noticeable improvement is obtained with respect to the calculation without linear momentum projection.

Massive quarks in neutron stars

We study various neutron star properties using the Color-Dielectric model to describe quark matter. For the baryon sector at low densities we employ the Walecka model. Applying Gibbs criteria to this composite system, we find that, for matter at β-equilibrium, the pure hadronic phase ends at 0.11 fm −3 and that the mixed quark and hadronic phase extends to 0.31 fm −3. The resulting equation of state yields a maximum neutron star mass of 1.59 M ⊙. A neutron star with total mass of 1.4 M ⊙ will consist of a crust made of hadronic matter only, a ∼ 1 km thick region of mixed phase and a core composed of pure quark matter. Implications for the cooling of neutron stars are discussed.

Magnetic moments of the octet baryons in the colour-dielectric model

Baryon magnetic moments are calculated in the colour-dielectric model with pion and kaon loops. The only free parameter of the model is determined from the nucleon isoscalar radius, and all SU(3) symmetry breaking, including that in the quark sector, is determined by mesonic masses and decay constants. Good agreement with experiment is obtained for the ratios of the magnetic moments, but the inclusion of kaons does not improve the results. The results obtained in this approach are significantly better than any that have been obtained in hedgehog-based models.

Neutron stars and massive quark matter

Using the Color-Dielectric model to describe quark confinement, including strange quarks and accounting for beta-equilibrium, we get masses for a static neutron star in the range 1.3 ≤ M M ⊙ ≤ 1.54 for a radius R ≈ 9 km.