Quark-meson Coupling Model Research Articles

In-Medium $$\varvec{\rho }$$ ρ -Meson Properties in a Light-Front Approach

Properties of \r{ho}-meson in symmetric nuclear matter are investigated within a light-front constituent quark model (LFCQM), using the in-medium input calculated by the quark-meson coupling (QMC) model. The LFCQM used here was previously applied in vacuum to calculate the \r{ho}-meson electromagnetic properties, namely, charge G 0 , magnetic G 1 , and quadrupole G 2 form factors, as well as the electromagnetic radius and decay constant. We predict the in-medium modifications of the \r{ho}-meson electromagnetic form factors in symmetric nuclear matter.

In-medium pion valence distributions in a light-front model

Pion valence distributions in nuclear medium and vacuum are studied in a light-front constituent quark model. The in-medium input for studying the pion properties is calculated by the quark-meson coupling model. We find that the in-medium pion valence distribution, as well as the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.

Reactions of exotic nuclei with the quark-meson coupling model

The nucleon-nucleon interaction is an important requirement for investigations of nuclear structure and reactions, as well as for astrophysical models such as r-process nucleosynthesis and neutron stars. The traditional approach to low-energy nuclear physics is to treat nucleons as immutable objects interacting via phenomenological forces. The use of phenomenological interactions, rather than one derived from a microscopic theory, raises questions as to the reliability of predictions for exotic regions of the nuclear chart. The quark-meson coupling (QMC) model uses a relativistic mean-field approach to provide a microscopically derived nucleon-nucleon interaction, which takes into account the quark structure of the nucleon.The Skyrme energy density functional is a popular phenomenological tool in studies of nuclear structure and reactions. In this work, the QMC density functional was used to produce a set of Skyrme parameterisations, in the hopes that they will give more reliable predictions for exotic nuclei. In conjunction with Hartree-Fock-Bogoliubov (HFB) calculations, the Skyrme-QMC (SQMC) parameterisations have been used to model the ground-state properties of individual nuclei and nucleus-nucleus potentials for Ca + Sn reactions. The SQMC parameterisation performs with an accuracy comparable to modern phenomenological functionals. From this, one can investigate the importance of the isovector terms of the nucleon-nucleon interaction, which are particularly significant for exotic, neutron-rich regions of the nuclear chart.One of the notable successes of the QMC model is its derivation of nuclear spin-orbit coupling. The isovector dependence of the spin-orbit equation of state is remarkably similar to that of the modern UNEDF1 phenomenological density functional. HFB calculations along the Sn isotopic chain reveal that the isovector properties of the spin-orbit term impact binding energies to a level that will be significant for astrophysical r-process modelling.

D¯D meson pair production in antiproton-nucleus collisions

We study the $\bar D D$ (${\bar D}^0 D^0$ and $D^-D^+$) charm meson pair production in antiproton (${\bar p}$) induced reactions on nuclei at beam energies ranging from threshold to several GeV. Our model is based on an effective Lagrangian approach that has only the baryon-meson degrees of freedom and involves the physical hadron masses. The reaction proceeds via the $t$-channel exchanges of $\Lambda_c^+$, $\Sigma_c^+$, and $\Sigma_c^{++}$ baryons in the initial collision of the antiproton with one of the protons of the target nucleus. The medium effects on the exchanged baryons are included by incorporating in the corresponding propagators, the effective charm baryon masses calculated within a quark-meson coupling (QMC) model. The wave functions of the bound proton have been determined within the QMC model as well as in a phenomenological model where they are obtained by solving the Dirac equation with appropriate scalar and vector potentials. The initial- and final-state distortion effects have been approximated by using an eikonal approximation-based procedure. Detailed numerical results are presented for total and double differential cross sections for the ${\bar D}^0 D^0$ and $D^-D^+$ production reactions on $^{16}$O and $^{90}$Zr targets. It is noticed that at ${\bar p}$ beam momenta of interest to the ${\bar P}ANDA$ experiment, medium effects lead to noticeable enhancements in the charm meson production cross sections.

Quark–meson coupling model based upon the Nambu–Jona Lasinio model

The NJL model for the octet baryons, using proper time regularization to simulate some of the features of confinement, is solved self-consistently in nuclear matter. This provides an alternative framework to the MIT bag model which has been used in the quark-meson coupling model. After fitting the parameters of the model to the saturation properties of symmetric nuclear matter the model is used to explore the equation of state of pure neutron matter as well as nuclear matter at densities relevant to heavy ion collisions. With a view to future studies of high mass neutron stars, the binding of hyperons is also explored.

Hyperon stars in a modified quark meson coupling model

We determine the equation of state (EOS) of nuclear matter with the inclusion of hyperons in a self-consistent manner by using a Modified Quark Meson Coupling Model (MQMC) where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $\sigma$, $\omega$, and $\rho$ mesons through mean-field approximations. The effect of a nonlinear $\omega$-$\rho$ term on the equation of state is studied. The hyperon couplings are fixed from the optical potential values and the mass-radius curve is determined satisfying the maximum mass constraint of $2$~M$_{\odot}$ for neutron stars, as determined in recent measurements of the pulsar PSR J0348+0432. We also observe that there is no significant advantage of introducing the nonlinear $\omega$-$\rho$ term in the context of obtaining the star mass constraint in the present set of parametrizations.

The effects of density-dependent form factors for (e, e’p) reaction in quasi-elastic region

Within the framework of a relativistic single particle model, the effects of density-dependent electromagnetic form factors on the exclusive $ (e,e'p)$ reaction are investigated in the quasi-elastic region. The density-dependent electromagnetic form factors are generated from a quark-meson coupling model and used to calculate the cross sections in two different densities, either at the normal density of $ \rho_0 \sim 0.15$ fm^-3 or at the lower density, $ 0.5\rho_0$ . Then these cross sections are analyzed in the two different kinematics: One is that the momentum of the outgoing nucleon is along the momentum transfer. The other is that the angle between the momentum of the outgoing nucleon and the momentum transfer is varied at fixed magnitude of the momentum of the outgoing nucleon. Our theoretical differential reduced cross sections are compared with the NIKHEF data for the 208 Pb(e, e’p) reaction, which is related to the probability that a bound nucleon from a given orbit can be knocked-out of the nucleus. The effects of the density-dependent form factors increase the differential cross sections for both knocked-out proton and neutron by an amount of a few percent. Moreover they are shown to be almost the same within only a few percent, i.e., nearly independent of the shell location of knockout nucleons. These results are quite consistent with the characteristics of double magic nuclei which have relatively sharp smearing in the density distribution.

Hybrid stars using the quark-meson coupling and proper-time Nambu–Jona-Lasinio models

Background: At high density deconfinement of hadronic matter may occur leading to quark matter. The immense densities reached in the inner core of massive neutron stars may be sufficient to facilitate the transition. Purpose: To investigate a crossover transition between two phenomenological models which epitomise QCD in two different regimes, while incorporating the influence of quark degrees of freedom in both. Method: We use the Hartree-Fock quark-meson coupling model and the proper time regularised three flavour NJL model to describe hadronic and quark matter, respectively. Hybrid equations of state are obtained by interpolating the energy density as a function of total baryonic density and calculating the pressure. Results: Equations of state for hadronic, quark and hybrid matter and the resulting mass versus radius curves for hybrid stars are shown, as well as other relevant physical quantities such as species fractions and the speed of sound in matter. Conclusions: The observations of massive neutron stars can certainly be explained within such a construction. However, the so-called thermodynamic correction arising from an interpolation method can have a considerable impact on the equation of state. The interpolation dependency of and physical meaning behind such corrections require further study.

Equation of State Grid with the Quark-Meson-Coupling Model

In this work we present the preliminary results of a complete equation of state (EoS) for core-collapse supernova simulations. We treat uniform matter made of nucleons using the the quark-meson coupling (QMC) model. We show a table with a variety of thermodynamic quantities, which covers the proton fraction range $Y_{p}=0-0.65$ with the linear grid spacing $ \Delta Y_{p}=0.01$ ($66$ points) and the density range $\rho_{B}=10^{14}-10^{16}$g.cm$^{-3}$ with the logarithmic grid spacing $\Delta log_{10}(\rho_{B}/[$g.cm$^{-3}])=0.1 $ ($21$ points). This preliminary study is performed at zero temperature and our results are compared with the widely used EoS already available in the literature.

EQUATION OF STATE FOR NEUTRON STARS WITH HYPERONS AND QUARKS IN THE RELATIVISTIC HARTREE–FOCK APPROXIMATION

We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark-meson coupling model with relativistic Hartree-Fock approximation, the EoS for hadronic matter is derived by taking into account the strange ($\sigma^{\ast}$ and $\phi$) mesons as well as the light non-strange ($\sigma$, $\omega$, $\vec{\pi}$ and $\vec{\rho}$) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector ($\phi$) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark-hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron star data.

Nuclear symmetry energy in a modified quark-meson coupling model

We study nuclear symmetry energy and the thermodynamic instabilities of asymmetric nuclear matter in a self-consistent manner by using a modified quark-meson coupling model where the confining interaction for quarks inside a nucleon is represented by a phenomenologically averaged potential in an equally mixed scalar-vector harmonic form. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to $\ensuremath{\sigma},\phantom{\rule{0.16em}{0ex}}\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons through mean-field approximations. We find an analytic expression for the symmetry energy ${\mathcal{E}}_{\mathrm{sym}}$ as a function of its slope $L$. Our result establishes a linear correlation between $L$ and ${\mathcal{E}}_{\mathrm{sym}}$. We also analyze the constraint on neutron star radii in $(pn)$ matter with $\ensuremath{\beta}$ equilibrium.

Effects of the cosmological constant on compact star in quark-meson coupling model

We study effect of the cosmological constant on compact star with equation of state provided by quark-meson coupling (QMC) model. In this model, baryons are described as a system of nonoverlapping bags interacting through the scalar and vector mesons. We derive the Tolman–Oppenheimer–Volkoff (TOV) equation taking into account the cosmological constant in static and spherically symmetric metric. Using the equation of state given by QMC model, the mass–radius relationship of the compact star has been computed for various values of the cosmological constant.

Density dependence of parity violation in electron quasi-elastic scattering

Within the framework of a relativistic single-particle model, we investigate the effect of the density dependent form factor on parity violating electron scattering from a heavy nucleus in the quasielastic region through the leading order of the interference of the electromagnetic current and the electro-weak neutral current. 208Pb is used as a target nucleus in the incident electron energy range up to 1 GeV. The density-dependent form factors are obtained from a quark-meson coupling model. The sensitivities of the density-dependence are studied separately for each Dirac (F 1), Pauli (F 2), and axial (G A ) form factors. The density enhances the parity violation asymmetry, in particular, in the forward angle region, and the density dependence turns out to be most sensitive to the Pauli form factor.

Open bottom mesons in a hot asymmetric hadronic medium

The in-medium masses and optical potentials of $B$ and ${\bar B}$ mesons are studied in an isospin asymmetric, strange, hot and dense hadronic environment using a chiral effective model. The chiral $SU(3)$ model originally designed for the light quark sector, is generalized to include the heavy quark sector ($c$ and $b$) to derive the interactions of the $B$ and ${\bar B}$ mesons with the light hadrons. Due to large mass of bottom quark, we use only the empirical form of these interactions for the desired purpose, while treating the bottom degrees of freedom to be frozen in the medium. Hence, all medium effects are due to the in-medium interaction of the light quark content of these open-bottom mesons. Both $B$ and $\bar B$ mesons are found to experience net attractive interactions in the medium, leading to lowering of their masses in the medium. The mass degeneracy of particles and antiparticles, ($B^+$, $B^-$) as well as ($B^0$, $\bar {B^0}$), is observed to be broken in the medium, due to equal and opposite contributions from a vectorial Weinberg-Tomozawa interaction term. Addition of hyperons to the medium lowers further the in-medium mass for each of these four mesons, while a non-zero isospin asymmetry is observed to break the approximate mass degeneracy of each pair of isospin doublets. These medium effects are found to be strongly density dependent, and bear a considerably weaker temperature dependence. The results obtained in the present investigation are compared to predictions from the quark-meson coupling model, heavy meson effective theory, and the QCD Sum Rule approach.

QCD symmetries and the η and η ′ in nuclei

We discuss the role of QCD symmetries in understanding the eta and etaprime mesons in nuclear media. Recent results on the etaprime mass in nuclei from the CBELSA/TAPS collaboration are very similar to the prediction of the Quark Meson Coupling model.

Effects of density-dependent weak form factors on neutral-current neutrino (antineutrino)-neucleus scattering in the quasi-elastic region

We study the effects of density-dependent weak vector form factors on the inclusive neutral-current--neutrino (antineutrino)-nucleus scattering in the quasi-elastic region within the framework of a relativistic single-particle model. The density-dependent weak form factors are obtained from a quark-meson coupling model. The density-dependence effects are studied separately in protons and neutrons participating in the reactions, in each response cross section, and with regard to asymmetry. These density effects reduce the cross section at high densities and show different behavior with regard to asymmetry. Furthermore we calculate flux-averaged differential cross sections and compare them with the experimental data.

Effect of Density-Dependent Form Factors on Coulomb Sum Rule in the Quasi-Elastic Region

Within the framework of a relativistic single particle model, we study the effects of density-dependent electromagnetic form factors on the inclusive (e,e′) reaction in the quasi-elastic region. The density-dependent form factors generated by a quark-meson coupling model are applied into the (e,e′) reaction. We calculate the differential cross sections, and extract the longitudinal and transverse structure functions. Furthermore the Coulomb sum is calculated in terms of three momentum transfer from 40Ca. The effects of the density-dependent form factors reduce the longitudinal structure function by amount of a few percent but increase the transverse structure function about 10%, consequently the (e,e′) differential cross sections are enhanced.

Pion structure in the nuclear medium

Using the light-front pion wave function based on a Bethe-Salpeter amplitude model, we study the properties of the pion in symmetric nuclear matter. The pion model we adopt is well constrained by previous studies to explain the pion properties in vacuum. In order to consistently incorporate the constituent up and down quarks of the pion immersed in symmetric nuclear matter, we use the quark-meson coupling model, which has been widely applied to various hadronic and nuclear phenomena in a nuclear medium with success. We predict the in-medium modifications of the pion lectromagnetic form factor, charge radius and weak decay constant in symmetric nuclear matter.

Effects of density-dependent weak form factors on charged-current neutrino-nucleus scattering in the quasi-elastic region

We study the effects of density-dependent electromagnetic, axial, and weak vector form factors on the inclusive $(e,{e}^{\ensuremath{'}})$ reaction and the charged-current neutrino-nucleus scattering in the quasi-elastic region within the framework of a relativistic single-particle model. The density-dependent form factors obtained from a quark-meson coupling model are applied into the $(e,{e}^{\ensuremath{'}})$ reaction and the neutrino-nucleus scattering via charged current. The effects of the density-dependent form factors increase the $(e,{e}^{\ensuremath{'}})$ cross sections by a few percent. However, the effects may reduce the differential cross sections up to 20% (60%) at $\ensuremath{\rho}=1.0{\ensuremath{\rho}}_{0}\phantom{\rule{4pt}{0ex}}(2.0{\ensuremath{\rho}}_{0})$ for the antineutrino scattering and also reduce the cross section up to 20% (30%) at $\ensuremath{\rho}=1.0{\ensuremath{\rho}}_{0}\phantom{\rule{4pt}{0ex}}(2.0{\ensuremath{\rho}}_{0})$ for the neutrino scattering around the peak positions, where the normal density is ${\ensuremath{\rho}}_{0}\ensuremath{\sim}0.15$ ${\mathrm{fm}}^{\ensuremath{-}3}$. For the density of finite nuclei such as $^{12}\mathrm{C}$, $^{40}\mathrm{Ca}$, and $^{208}\mathrm{Pb}$ as 0.6, 0.7, and 1.0 of ${\ensuremath{\rho}}_{0}$, the in-medium effects are 20% to 30%, even in the antineutrino case. Our theoretical double-differential and total cross sections are compared with the recent MiniBooNE data for $^{12}\mathrm{C}({\ensuremath{\nu}}_{\ensuremath{\mu}},{\ensuremath{\mu}}^{\ensuremath{-}})$ scattering.

Quark-meson coupling model, nuclear matter constraints, and neutron star properties

We explore the equation of state for nuclear matter in the quark-meson coupling model, including full Fock terms. The comparison with phenomenological constraints can be used to restrict the few additional parameters appearing in the Fock terms which are not present at Hartree level. Because the model is based upon the in-medium modification of the quark structure of the bound hadrons, it can be applied without additional parameters to include hyperons and to calculate the equation of state of dense matter in beta-equilibrium. This leads naturally to a study of the properties of neutron stars, including their maximum mass, their radii and density profiles.