Quark-meson Coupling Research Articles

Kaon Condensation in a Neutron Star under Strong Magnetic Fields by Using the Modifid Quark-meson Coupling Model

We have considered the antikaon condensation in a neutron star in the presence of strong magnetic fields by using the modified quark-meson coupling (MQMC) model. The structure of the neutron star is investigated with various magnetic fields and different kaon optical potentials, and the effects of the magnetic fields for kaon condensation is discussed. When employing strong magnetic fields inside a neutron star with hyperons and kaon condensation, the magnetic fields can cause the equation of state to be stiff; thus, a large maximum mass of the neutron star can be obtained.

Kaon Condensation in the Neutron Star with a Quark-Meson Coupling Model

Kaon Condensation in the Neutron Star with a Quark-Meson Coupling Model

J/Ψ-nuclear bound states

$J/\Psi$-nuclear bound state energies are calculated for a range of nuclei by solving the Proca (Klein-Gordon) equation. Critical input for the calculations, namely the medium-modified $D$ and $D^*$ meson masses, as well as the nucleon density distributions in nuclei, are obtained from the quark-meson coupling model. The attractive potential originates from the $D$ and $D^*$ meson loops in the $J/\Psi$ self-energy in nuclear medium. It appears that $J/\Psi$-nuclear bound states should produce a clear experimental signature provided that the $J/\Psi$ meson is produced in recoilless kinematics.

Formula omitted] mass shift in nuclear matter

The J/Ψ mass shift in cold nuclear matter is computed using an effective Lagrangian approach. The mass shift is computed by evaluating D and D⁎ meson loop contributions to the J/Ψ self-energy employing medium-modified meson masses. The modification of the D and D⁎ masses in nuclear matter is obtained using the quark–meson coupling model. The loop integrals are regularized with dipole form factors and the sensitivity of the results to the values of form-factor cutoff masses is investigated. The J/Ψ mass shift arising from the modification of the D and D⁎ loops at normal nuclear matter density is found to range from −16 MeV to −24 MeV under a wide variation of values of the cutoff masses. Experimental perspectives for the formation of a bound state of J/Ψ to a nucleus are investigated.

THE STRUCTURE OF NEUTRON STAR BY USING THE QUARK-MESON COUPLING MODEL

We investigate the structure of neutron star within the framework of the quark-meson coupling model, considering hyperons and kaon condensation. In order to compare the EoS with that from quark matter, the MIT bag model is used. We calculate the mass and radius of a neutron star by using Tolman-Oppenheimer-Volkov equations.

BINDING OF HYPERNUCLEI, AND PHOTOPRODUCTION OF Λ-HYPERNUCLEI IN THE LATEST QUARK-MESON COUPLING MODEL

We study the binding of hypernuclei based on the latest version of quark-meson coupling model, and estimate the photoproduction cross sections for the [Formula: see text] reaction using the bound Λ spinors obtained in the model.

δ MESON EFFECTS ON NEUTRON STARS IN THE MODIFIED QUARK–MESON COUPLING MODEL

The properties of neutron stars are investigated by including δ meson field in the modified quark–meson coupling model. It is found that δ meson has opposite effects on hadronic matter with or without hyperons: it softens the EOSs of hadronic matter with hyperons, while it stiffens the EOSs of pure nucleonic matter. Moreover, by replacing the isovector mesons with the contact scalar–isovector interaction, a considerable change of proton fraction is observed. It is shown that the contact scalar–isovector interaction provides an approach to satisfy the constraint of Direct Urca critical star masses. However, the inclusion of δ meson increases the proton fraction, consequently it decreases the M DU which departs farther from the Direct Urca constraint. Furthermore, the inclusion of δ meson field can increase the maximum mass of neutron star and enlarge the corresponding radius, while these quantities are decreased when the contact scalar–isovector interaction is included.

Warm stellar matter within the quark-meson-coupling model

In the present article, we investigate stellar matter obtained within the quark-meson-coupling (QMC) model for fixed temperature and with the entropy of the order of $1$ or $2$ Boltzmann units per baryon for neutrino-free matter and matter with trapped neutrinos. A new prescription for the calculation of the baryon effective masses in terms of the free energy is used. Comparing the results of the present work with those obtained from the nonlinear Walecka model, smaller strangeness and neutrino fractions are predicted within QMC. As a consequence, QMC has a smaller window of metastability for conversion into a low-mass blackhole during cooling.

Polarization Transfer in theHe4(e→,e′p→)H3Reaction atQ2=0.8and1.3 (GeV/c)2

Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the 1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation, and favoring either the inclusion of medium-modified proton form factors predicted by the quark-meson coupling model or a spin-dependent charge-exchange final-state interaction. For the first time, the polarization-transfer ratio is studied as a function of the virtuality of the proton.

Magnetic moments of octet baryons at finite density and temperature

We investigate the change of magnetic moments of octet baryons in nuclear matter at a finite density and temperature. Quark–meson coupling (QMC) models are employed in describing the properties of octet baryons and their interactions. Magnetic moments of octet baryons are found to increase non-negligibly as density and temperature increase, and we find that the temperature dependence can be strongly correlated with the quark–hadron phase transition. The model dependence is also examined by comparing the results from the QMC model to those from the modified QMC (MQMC) model where the bag constant is assumed to depend on density. Both models predict sizable dependence on density and temperature, but the MQMC model shows a more drastic change of magnetic moments. Feasible changes of the nucleon mass by strong magnetic fields are also reported for the given models.

Nuclear matter and neutron matter for an improved quark mass density-dependent model with ρ mesons

A new improved quark mass density-dependent model including u, d quarks, σ mesons, ω mesons and ρ mesons is presented. By employing this model, the properties of nuclear matter, neutron matter and neutron star are studied. After introducing the isovector ρ mesons, the isospin effect for asymmetric nuclear matter is considered. Under mean field approximation, we find that our model can describe the properties of asymmetric nuclear matter, in particular the neutron matter, successfully. The results given by the new improved quark mass density-dependent model and by the quark–meson coupling model are compared.

Particle production within the quark meson coupling model

Quark-meson coupling (QMC) models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter. In the regime of hot hadronic matter very few calculations exist using the QMC model, in particular when applied to particle yields in heavy ion collisions. In the present work, we identify the free energy of the bag with the effective mass of the baryons and we calculate the particle production yields on a $\mathrm{Au}+\mathrm{Au}$ collision at the BNL Relativistic Heavy Ion Collider (RHIC) with the QMC model and compare them with results obtained previously with other relativistic models. A smaller temperature for the fireball, $T=132$ MeV, is obtained because of the smaller effective baryon masses predicted by QMC. QMC was also applied to the description of particle yields at the CERN Super Proton Synchrotron (SPS) in $\mathrm{Pb}+\mathrm{Pb}$ collisions.

Medium modifications of the bound nucleon generalized parton distributions and the quark contribution to the spin sum rule

We estimate the nuclear medium modifications of the quark contribution to the bound nucleon spin sum rule, ${J}^{{q}^{*}}$, as well the separate helicity, $\ensuremath{\Delta}{\ensuremath{\Sigma}}^{*}$, and the angular momentum, ${L}^{{q}^{*}}$, contributions to ${J}^{{q}^{*}}$. For the calculation of the bound nucleon generalized parton distributions (GPDs), we use as input the bound nucleon elastic form factors predicted in the quark-meson coupling model. Our model for the bound nucleon GPDs is relevant for incoherent deeply virtual Compton scattering (DVCS) with nuclear targets. We find that the medium modifications increase ${J}^{{q}^{*}}$ and ${L}^{{q}^{*}}$ and decrease $\ensuremath{\Delta}{\ensuremath{\Sigma}}^{*}$ compared to the free nucleon case. The effect is large and increases with increasing nuclear density \ensuremath{\rho}. For instance, at $\ensuremath{\rho}={\ensuremath{\rho}}_{0}=0.15 {\mathrm{fm}}^{\ensuremath{-}3},{J}^{{q}^{*}}$ increases by 7%, ${L}^{{q}^{*}}$ increases by 20%, and $\ensuremath{\Delta}{\ensuremath{\Sigma}}^{*}$ decreases by 17%. These in-medium modifications of the bound nucleon spin properties are a general feature of relativistic mean-field quark models and may be understood qualitatively in terms of the enhancement of the lower component of the quark Dirac spinor in the nuclear medium.

Photoproduction of hypernuclei within the quark–meson coupling model

We study the photoproduction of the 12ΛB hypernucleus within a fully covariant effective Lagrangian based model, employing Λ bound state spinors derived from the latest quark–meson coupling model. The kaon production vertex is described via creation, propagation and decay of N∗(1650), N∗(1710), and N∗(1720) intermediate baryonic resonant states in the initial collision of the photon with a target proton in the incident channel. The parameters of the resonance vertices are fixed by describing the total and differential cross section data on the elementary γp→ΛK+ reaction in the energy regime relevant to the hypernuclear production. It is found that the hypernuclear production cross sections calculated with the quark model based hyperon bound state spinors differ significantly from those obtained with the phenomenological Dirac single particle wave functions.

Phase transition from quark-meson coupling hyperonic matter to deconfined quark matter

We investigate the possibility and consequences of phase transitions from an equation of state (EOS) describing nucleons and hyperons interacting via mean fields of $\ensuremath{\sigma}$, $\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons in the recently improved quark-meson coupling (QMC) model to an EOS describing a Fermi gas of quarks in an MIT bag. The transition to a mixed phase of baryons and deconfined quarks, and subsequently to a pure deconfined quark phase, is described using the method of Glendenning. The overall EOS for the three phases is calculated for various scenarios and used to calculate stellar solutions using the Tolman-Oppenheimer-Volkoff equations. The results are compared with recent experimental data, and the validity of each case is discussed with consequences for determining the species content of the interior of neutron stars.

Low density instabilities in asymmetric nuclear matter within the quark-meson coupling (QMC) model with the δ meson

In the present work we include the isovector-scalar {delta} meson in the quark-meson coupling (QMC) model and study the properties of asymmetric nuclear within QMC without and with the {delta} meson. Recent constraints set by isospin diffusion on the slope parameter of the nuclear symmetry energy at saturation density are used to adjust the model parameters. The thermodynamical spinodal surfaces are obtained and the instability region at subsaturation densities within QMC and QMC{delta} models are compared with mean-field relativistic models. The distillation effect in the QMC model is discussed.

Effect of Gluon and Pion Exchanges on Hyperons in Nuclear Matter

A new version of the quark-meson coupling model, in which the effect of gluon and pion exchanges is included self-consistently, is applied to hyperons in a nuclear medium. The hyperfine interaction due to the gluon exchange plays an important role in the in-medium baryon spectra, while the pion-cloud effect is relatively small. At the quark mean-field level, the Λ feels more attractive force than the Σ or Ξ in matter. Subject Index: 211, 214

Magnetic moment of hyperons in nuclear matter by using quark–meson coupling models

We calculate the magnetic moments of hyperons in dense nuclear matter by using relativistic quark models. Hyperons are treated as MIT bags, and the interactions are considered to be mediated by the exchange of scalar and vector mesons which are approximated as mean fields. Model dependence is investigated by using the quark–meson coupling model and the modified quark–meson coupling model; in the former the bag constant is independent of density and in the latter it depends on density. Both models give us the magnitudes of the magnetic moments increasing with density for most octet baryons. But there is a considerable model dependence in the values of the magnetic moments in dense medium. The magnetic moments at the nuclear saturation density calculated by the quark–meson coupling model are only a few percents larger than those in free space, but the magnetic moments from the modified quark–meson coupling model increase more than 10% for most hyperons. The correlations between the bag radius of hyperons and the magnetic moments of hyperons in dense matter are discussed.

Dmesons in asymmetric nuclear matter

We calculate the in-medium $D$ and $\overline{D}$ meson masses in isospin-asymmetric nuclear matter in an effective chiral model. The $D$ and $\overline{D}$ mass modifications arising from their interactions with the nucleons and the scalar mesons in the effective hadronic model are seen to be appreciable at high densities and have a strong isospin dependence. These mass modifications can open the channels of the decay of the charmonium states $({\ensuremath{\Psi}}^{'},{\ensuremath{\chi}}_{c},J/\ensuremath{\Psi})$ to $D\overline{D}$ pairs in dense hadronic matter. The isospin asymmetry in the doublet $D=({D}^{0},{D}^{+})$ is seen to be particularly appreciable at high densities and should show in observables such as their production and flow in asymmetric heavy-ion collisions in the compressed baryonic matter experiments in the future facility of FAIR, GSI. The results of the present work are compared to calculations of the $D(\overline{D}$) in-medium masses in the literature using the QCD sum rule approach, quark meson coupling model, and coupled channel approach as well as to those from studies of quarkonium dissociation using heavy-quark potentials from lattice QCD at finite temperatures.

Medium modifications of the bound nucleon GPDs and incoherent DVCS on nuclear targets

We study incoherent DVCS on 4He in the He4(e,e′γp)X reaction, which probes possible medium-modifications of the bound nucleon GPDs and elastic form factors. Assuming that the bound nucleon GPDs are modified in proportion to the corresponding bound nucleon elastic form factors, as predicted in the quark–meson coupling model, we develop an approach to calculate various incoherent nuclear DVCS observables. As an example, we compute the beam-spin DVCS asymmetry, and predict the xB- and t-dependence of the ratio of the bound to free proton asymmetries, ALUp*(ϕ)/ALUp(ϕ). We find that the deviation of ALUp*(ϕ)/ALUp(ϕ) from unity is as much as ∼6%.