Chiral 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.

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

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.

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).

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.

Hybrid stars and quark hadron phase transition in chiral colour dielectric model

We investigate the properties of hybrid stars consisting of quark matter in the core and hadron matter in outer region. The hadronic and quark matter equations of state are calculated by using nonlinear Walecka model and chiral colour dielectric (CCD) model respectively. We find that the phase transition from hadron to quark matter is possible in a narrow range of the parameters of nonlinear Walecka and CCD models. The transition is strong or weak first order depending on the parameters used. The EOS thus obtained, is used to study the properties of hybrid stars. We find that the calculated hybrid star properties are similar to those of pure neutron stars.

Three-flavor quark matter in the chiral color dielectric model.

We investigate the properties of quark matter at finite density and temperature using the nonlinear chiral extension of Colour Dielectric Model (CCM). Assuming that the square of the meson fields devlop non- zero vacuum expectation value, the thermodynamic potential for interacting three flavour matter has been calculated. It is found that $ $ and $ $ remain zero in the medium whereas $ $ changes in the medium. As a result, $u$ and $d$ quark masses decrease monotonically as the temperature and density of the quark matter is increased.In the present model, the deconfinement density and temperature is found to be lower compared to lattice results. We also study the behaviour of pressure and energy density above critical temperature.

CHARGE RADII OF HYPERONS

The momentum projected SU(3) chiral color dielectric model (CCDM) is employed to calculate the charge root mean square radii and charge distribution of hyperons. The gluonic and pionic contributions are treated perturbatively. We compare our result with that of Skyrme, MIT bag and cloudy bag model. The charge distribution of Λ in CCDM is similar to that of Skyrme model prediction.

Quark matter in the chiral color-dielectric model

We study the equation of state of quark matter at zero temperature, using the chiral-invariant color dielectric model to describe confinement. An exhaustive analysis of the various versions of the model has been performed, and the results are shown to discriminate among them. The deconfinement phase transition turns out to be smooth. Deconfinement and chiral symmetry restoration occur at very different densities. Instabilities of the quark matter and the gap equation are also discussed.

Pion-nucleon scattering and the pi NN coupling constant in the chiral color dielectric model.

We apply the chiral color dielectric model to low- and medium-energy scattering within the coupled $\pi$N and $\pi\Delta$ system. Dynamic baryon states in which quarks are confined by the scalar color-dielectric field are constructed in Fock space. Spurious motion of the center of mass is eliminated by constructing momentum eigenstates via a Peierls-Yoccoz projection. The relativistic Lippmann-Schwinger equation is solved for the complex energies of the T matrix poles, and the pole positions of the nucleon and delta are used to fix the few parameters of the model. The $S$- and $P$-wave phase shifts, the bare N and $\Delta$ masses, the renormalized $\pi$NN and $\pi$N$\Delta$ coupling constants, and the $\pi$NN and $\pi$N$\Delta$ vertex functions are predicted. nucleon and delta are used to fix the few parameters of the model. The $S$- and $P$-wave phase shifts, the bare N and $\Delta$ masses, the renormalized $\pi$NN and $\pi$N$\Delta$ coupling constants, and the $\pi$NN and $\pi$N$\Delta$ vertex functions are predicted.

The strangeness content of the nucleon

The strangeness content of the nucleon is estimated in the SU(3) chiral color dielectric model where the pseudoscalar meson contribution is treated perturbatively. The strangeness content is generated by including the kaon and eta cloud in the calculation. The calculation shows that the probability of the kaon and eta cloud varies between 1.2% and 3.9% for different parameter sets. The contribution of the strange sector to the nucleon properties is less than 4%.

Chiral color-dielectric model with perturbative quantum pions and gluons.

Pionic contributions to static nucleon properties are calculated in a chiral extension of the color-dielectric model. The pion field and residual gluon field are treated perturbatively. It is shown that with a simple choice for the energy of the scalar confining field and assuming the chiral limit, the system of equations describing the bare soliton and the perturbative pion and gluon fields may be cast in a dimensionless, parameter-free form for large glueball masses. This enables a formula for the masses of the nucleon and \ensuremath{\Delta} including leading-order pionic and gluonic contributions and corrections for spurious center-of-mass motion, valid for a wide range of input parameters determining the bare-soliton solutions, to be derived. A further consequence of the scaling behavior is that pionic contributions to nucleon properties, calculated using the methods of the cloudy-bag model, are insensitive to the soliton parameters, once the size of the soliton is fixed. The model results are very similar to those of the cloudy-bag model but the predicted masses are about 20% too large, and the pionic contributions to charge radii are underestimated.

Study of quark matter in the chiral colour dielectric model

The non-linear chiral extension of the colour dielectric model has been used to study the properties for quark matter. Assuming that the square of the pion field develops non-zero vacuum expectation value, the thermodynamic potential for interacting two-flavour quark matter has been calculated up to second order in interaction terms of the Lagrangian. The values of the colour dielectric field and ( pi 2) in quark matter are obtained by solving mean field equations. It is found that, because of non-zero ( pi 2) the quark mass decreases monotonically as the temperature and density of the quark matter are increased. The calculated transition temperature and density for deconfinement transition have been found to be smaller than the lattice-QCD results. The behaviour of pressure and energy density of the quark matter calculated is qualitatively similar to that obtained in lattice-QCD calculations.

Chiral colour dielectric model of the nucleon

Abstract We apply the colour dielectric model to the nucleon including the chiral symmetry by the linear sigma model. The results of numerical calculations show that as the quark-meson coupling becomes stronger, the chiral symmetry breaking phase inside the bag changes to the restoring phase. The hedgehog solution is projected onto the spin-isospin eigenstate by means of the collective coordinate method, and we study some static properties of the nucleon. Except for the proton magnetic moment, the observed static properties favour strong quark-meson coupling and light glueball mass (∼1 GeV) giving a “chiral bag” like solution. The calculated values of the observables are similar to those of the chiral soliton bag model with the topological number: Z = 1.

A Chiral Colour Dielectric Model of the Nucleon

A Chiral Colour Dielectric Model of the Nucleon