Quark-meson Coupling Model Research Articles

Quark-meson coupling model for antikaon condensation in neutron star matter with strong magnetic fields

We study the effects of strong magnetic fields on antikaon condensation in neutron star matter using the quark-meson coupling (QMC) model. The QMC model describes a nuclear many-body system as nonoverlapping MIT bags in which quarks interact through the self-consistent exchange of scalar and vector mesons in the mean-field approximation. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly. The onset of K{sup -} condensation stronger depends on the magnetic field strength, and it even shifts beyond the threshold of K{sup 0} condensation for sufficiently strong magnetic fields. In the presence of strong magnetic fields, the equation of state (EOS) becomes stiffer in comparison with the field-free case. The softening of the EOS by antikaon condensation also depends on the magnetic field strength, and it becomes less pronounced with increasing magnetic field strength. The results of the QMC model are compared with those obtained in a relativistic mean-field (RMF) model, and we find there are quantitative differences between the results of the QMC and RMF models.

Metastability of hadronic compact stars

Pure hadronic compact stars, above a threshold value of their gravitational mass (central pressure), are metastable to the conversion to quark stars (hybrid or strange stars). In this paper, we present a systematic study of the metastability of pure hadronic compact stars using different relativistic models for the equation of state. In particular, we compare results for the quark-meson coupling model with those for the Glendenning-Moszkowski parametrization of the nonlinear Walecka model. For the quark-meson coupling model, we find large values (${M}_{\mathrm{cr}}=1.6--1.9{M}_{\ensuremath{\bigodot}}$) for the critical mass of the hadronic star sequence and we find that the formation of a quark star is only possible with a soft quark matter equation of state. For the Glendenning-Moszkowski parametrization of the nonlinear Walecka model, we explore the effect of different hyperon couplings on the critical mass and on the stellar conversion energy. We find that increasing the value of the hyperon coupling constants shifts the bulk transition point for quark deconfinement to higher densities, increases the stellar metastability threshold mass and the value of the critical mass, and thus makes the formation of quark stars less likely. For the largest values of the hyperon couplings we find a critical mass which may be as high as $1.9--2.1{M}_{\ensuremath{\bigodot}}$. These stellar configurations, which contain a large central hyperon fraction (${f}_{Y,\mathrm{cr}}\ensuremath{\sim}30%$), would be able to describe highly massive compact stars, such as the one associated with the millisecond pulsar PSR $\mathrm{B}1516+02\mathrm{B}$ with a mass $M={1.94}_{\ensuremath{-}0.19}^{+0.17}{M}_{\ensuremath{\bigodot}}$.

Improved density-dependent quark mass model with quark-σ meson and quark-ω meson couplings

We present an improved quark mass density-dependent model with the nonlinear scalar sigma field and the \ensuremath{\omega}-meson field. By comparing with the quark-meson coupling model, we show that our model can successfully describe saturation properties, the equation of state, the compressibility and the effective nuclear mass of nuclear matter under the mean field approximation.

Quark deconfinement in neutron star cores

Whether or not the deconfined quark phase exists in neutron star cores is an open question. We use two realistic effective quark models, the three-flavor Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to describe the neutron star matter. We show that the modified quark-meson coupling model, which is fixed by reproducing the saturation properties of nuclear matter, can be consistent with the experimental constraints from nuclear collisions. After constructing possible hybrid equations of state (EOSes) with an unpaired or color superconducting quark phase with the assumption of the sharp hadron-quark phase transition, we discuss the observational constraints from neutron stars on the EOSes. It is found that the neutron star with pure quark matter core is unstable and the hadronic phase with hyperons is denied, while hybrid EOSes with a two-flavor color superconducting phase or unpaired quark matter phase are both allowed by the tight and most reliable constraints from two stars Ter 5 I and EXO 0748-676. And the hybrid EOS with an unpaired quark matter phase is allowed even compared with the tightest constraint from the most massive pulsar star PSR J0751+1807.

Cold uniform matter and neutron stars in the quark–meson-coupling model

A new density dependent effective baryon–baryon interaction has been recently derived from the quark–meson-coupling (QMC) model, offering impressive results in application to finite nuclei and dense baryon matter. This self-consistent, relativistic, quark-level approach is used to construct the Equation of State (EoS) and to calculate key properties of high density matter and cold, slowly rotating neutron stars. The results include predictions for the maximum mass of neutron-star models, together with the corresponding radius and central density, as well the properties of neutron stars with mass of order 1.4 M ⊙ . Some conditions related to the direct URCA process are explored for the QMC EoS and the parameters relevant to slow rotation, namely the moment of inertia and the period of rotation, are investigated. The results of the calculation, which are found to be in good agreement with available observational data, are compared with the predictions of several more traditional EoS. The QMC EoS provides cold neutron-star models with maximum mass in the range 1.9–2.1 M ⊙ , with central density less than 6 times nuclear saturation density ( n 0 = 0.16 fm −3 ) and offers a consistent description of the stellar mass up to this density limit. In contrast with other models, QMC predicts no hyperon contribution at densities lower than 3 n 0 , for matter in β-equilibrium. At higher densities, Ξ − , 0 and Λ hyperons are present, with consequent lowering of the maximum mass. The absence of lighter Σ ± , 0 hyperons is understood as consequence of including the color hyperfine interaction in the response of the quark bag to the nuclear scalar field.

Kaon condensation and composition of neutron star matter in a modified quark-meson coupling model

We use the modified quark-meson coupling (MQMC) model to study the composition profile of neutron star matter and compare the results with those calculated by quantum hadrodynamics (QHD). Both MQMC and QHD model parameters are adjusted to produce exactly the same saturation properties so that we can investigate the model dependences of the matter composition at high densities. We consider the possibility of deep kaon optical potential and find that the composition of matter is very sensitive to the interaction strength of kaons with matter. The onset densities of the kaon condensation are studied in detail by varying the kaon optical potentials. We find that the MQMC model produces the kaon condensation at lower densities than QHD. The presence of kaon condensation changes drastically the population of octet baryons and leptons. Once the kaon condensation takes place, the population of kaons builds up very quickly, and kaons become the dominant component of the matter. We find that the $\omega$-meson plays an important role in increasing the kaon population and suppressing the hyperon population.

Landau parameters for isospin asymmetric nuclear matter based on a relativistic model of composite and finite extension nucleons

We study the properties of cold asymmetric nuclear matter at high density, applying the quark meson coupling model with excluded volume corrections in the framework of the Landau theory of relativistic Fermi liquids. We discuss the role of the finite spatial extension of composite baryons on dynamical and statistical properties such as the Landau parameters, the compressibility, and the symmetry energy. We have also calculated the low-lying collective eigenfrequencies arising from the collisionless quasiparticle transport equation, considering both unstable and stable modes. An overall analysis of the excluded volume correlations on the collective properties is performed.

Nucleon sigma term and quark condensate in nuclear matter

We study the bound nucleon sigma term and the quark condensate in nuclear matter. In the quark-meson coupling (QMC) model the nuclear correction to the sigma term is small and negative, i.e., it decelerates the decrease of the quark condensate in nuclear matter. However, the quark condensate in nuclear matter is controlled primarily by the scalar-isoscalar $\sigma$ field. Compared to the leading term, it moderates the decrease more than that of the nuclear sigma term alone at densities around and larger than the normal nuclear matter density.

Origin of the Nuclear Equation of State at the Quark Level

At the present time there is a lively debate within the nuclear community concerning the relevance of quark degrees of freedom in understanding nuclear structure. We outline the key issues and review the impressive progress made recently within the framework of the quark-meson coupling model. In particular, we explain in quite general terms how the modification of the internal structure of hadrons in-medium leads naturally to three- and four-body forces, or equivalently, to density dependent effective interactions.

Neutron star matter in the quark-meson coupling model in strong magnetic fields

The effects of strong magnetic fields on neutron star matter are investigated in the quark-meson coupling (QMC) model. The QMC model describes a nuclear many-body system as nonoverlapping MIT bags in which quarks interact through self-consistent exchange of scalar and vector mesons in the mean-field approximation. The results of the QMC model are compared with those obtained in a relativistic mean-field (RMF) model. It is found that quantitative differences exist between the QMC and RMF models, whereas qualitative trends of the magnetic-field effects on the equation of state and composition of neutron star matter are very similar.

Physical origin of density dependent forces of Skyrme type within the quark meson coupling model

A density dependent, effective nucleon–nucleon force of the Skyrme type is derived from the quark–meson coupling model—a self-consistent, relativistic quark level description of nuclear matter. This new formulation requires no assumption that the mean scalar field is small and hence constitutes a significant advance over earlier work. The similarity of the effective interaction to the widely used SkM ∗ force encourages us to apply it to a wide range of nuclear problems, beginning with the binding energies and charge distributions of doubly magic nuclei. Finding acceptable results in this conventional arena, we apply the same effective interaction, within the Hartree–Fock–Bogoliubov approach, to the properties of nuclei far from stability. The resulting two neutron drip lines and shell quenching are quite satisfactory. Finally, we apply the relativistic formulation to the properties of dense nuclear matter in anticipation of future application to the properties of neutron stars.

Rotating compact star with superconducting quark matter

A compact star with a superconducting quark core, a hadron crust, and a mixed phase between the two is considered. The quark-meson coupling model for hadron matter and the color-flavor-locked quark model for quark matter is used to construct the equation of state for the compact star. The effect of pairing of quarks in the color-flavor-locked phase and the mixed phase on the mass, radius, and period of the rotating star is studied.

γ-ray bursts and the QCD phase diagram

The quantum chromodynamics phase diagram shows the phase transitions that can take place in matter at different temperatures and densities. In this work we discuss the possibility that \ensuremath{\gamma}-ray bursts might result from a phase change in the interior of a neutron star and calculate the energy released in the conversion of a metastable star into a stable star. We consider several different initial and several different final configurations. Initial metastable stars are taken as hadronic, hybrid, and quark stars with unpaired quarks; possible stable stars are hybrid and quark stars, taken both with unpaired and paired phases to study the deconfinement phase transition and normal quark matter--superconducting quark matter phase transition within a large number of relativistic models used to describe compact stars. The models used for the hadron matter are the nonlinear Walecka model and the quark-meson coupling model with and without hyperons. For the quark matter we have used the MIT bag model, the bag model with paired quarks to which we refer as the color-flavor-locked phase model, and the Nambu--Jona-Lasinio model. Within this mechanism we obtain energies of the order of ${10}^{50}\ensuremath{-}{10}^{53}$ erg, accounting for both long and short \ensuremath{\gamma}-ray bursts.

Neutron star composition with strange hadrons in the modified quark-meson coupling model(Hadrons at finite density)

Neutron star composition with strange hadrons in the modified quark-meson coupling model(Hadrons at finite density)

Pentaquarks in the medium in the quark-meson coupling model

We calculate the properties of the pentaquarks ${\ensuremath{\Theta}}^{+}$ and ${\ensuremath{\Xi}}^{\ensuremath{-}\ensuremath{-},0}$ in symmetric nuclear matter using the quark-meson coupling model (QMC). The stability of the ${\ensuremath{\Theta}}^{+}$ in the medium with respect to the channel ${\ensuremath{\Theta}}^{+}\ensuremath{\rightarrow}{\mathit{NK}}^{+}$ is discussed.

Effective mass and decay ofΘ+in nuclear matter by using the quark-meson coupling models

The in-medium mass of a ${\ensuremath{\Theta}}^{+},{m}_{{\ensuremath{\Theta}}^{+}}^{*}$, in cold symmetric nuclear matter is calculated by use of the quark-meson coupling models. The ${\ensuremath{\Theta}}^{+}$ is treated as an MIT bag with a quark content $\mathit{uudd}\overline{s}$. The bag parameters for a free ${\ensuremath{\Theta}}^{+}$ are fixed to reproduce the observed mass of the ${\ensuremath{\Theta}}^{+}$. In doing so, we use three different values of the s-quark mass as the mass of the s quark is not well known. As usual, the strengths of the u- and d-quark couplings to \ensuremath{\sigma}- and \ensuremath{\omega}-meson fields are determined to fit the nuclear saturation properties. However, the coupling constant ${g}_{\ensuremath{\sigma}}^{s}$ between the s quark and the \ensuremath{\sigma} meson cannot be fixed from the saturation properties, and thus we treat ${g}_{\ensuremath{\sigma}}^{s}$ as a free parameter and investigate how ${m}_{{\ensuremath{\Theta}}^{+}}^{*}$ depends on ${g}_{\ensuremath{\sigma}}^{s}$. We find that ${m}_{{\ensuremath{\Theta}}^{+}}^{*}$ depends significantly on the value of ${g}_{\ensuremath{\sigma}}^{s}$ but not on the mass of the s quark. Chemical potentials of the ${\ensuremath{\Theta}}^{+}$ and the $K+N$ system are calculated to discuss the decay of a ${\ensuremath{\Theta}}^{+}$ in nuclear matter. We calculate the effective mass of a kaon in nuclear matter in two ways: by using the optical potential of ${K}^{\ensuremath{-}}$ in matter and by using a quark model. By comparing the effective masses of K calculated from these two methods, we find that the magnitude of the real part of the optical potential that is consistent with the quark model is about 100 MeV. In that case, we find ${g}_{\ensuremath{\sigma}K}\ensuremath{\approx}2$.

Kaon condensation in the quark-meson coupling model and compact stars

The properties of neutron stars, consisting of a crust of hadrons and an internal part of hadrons and kaon condensate, are calculated within the quark-meson-coupling model. We considered stars with nucleons only in the hadron phase and also stars with hyperons as well. The results are compared with the ones obtained from the nonlinear Walecka model for the hadronic phase.

Thermal kaon production in relativistic heavy-ion collisions

We study kaon production in hot and dense hypernuclear matter with a conserved zero total strangeness and a conserved small negative isospin charge fraction in order to make our results relevant to relativistic heavy-ion collisions. The baryons and kaons are treated as MIT bags in the context of the modified quark–meson coupling model. They interact with each other via the scalar mesons σ, σ ∗ and the vector mesons ω, ϕ as well as the isovector meson ρ. We adopt realistic sets of hyperon–hyperon interactions based on several versions of the Nijmegen core potential models. Our results indicate that the hyperons as well as the kaons are produced abundantly when the temperature increases and approaches the critical temperature for the phase transition to a quark–gluon plasma. Moreover we find that the kaons are only produced thermally and we find no kaon condensation in the regime explored by relativistic heavy-ion collisions.

Hadron masses in medium and neutron star properties

We investigate the properties of the neutron star with relativistic mean-field models. We incorporate in the quantum hadrodynamics and in the quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is obtained and is employed in Oppenheimer-Volkov equation to extract the maximum mass of the stable neutron star. We find that the equation of state, the composition and the properties of the neutron stars are sensitive to the values of the meson masses in medium.

Θ+hypernuclei in relativistic mean-field model

We have investigated the properties of $\Theta^{+}$ in nuclei within the framework of relativistic mean field. The coupling constants are educed with quark meson coupling model. There is strong attractive interaction for $\Theta^{+}$-nucleus and $\Theta^{+}$ can be bind in nuclei. The depth of optical potential for $\Theta^{+}$ in nuclear matter is estimated.