Quark-meson <Emphasis Type="Italic">SU</Emphasis>(3) model in a Tamm-Dancoff inspired approximation

The non-linear chiral quark-meson U(3) x U(3) model is solved using the Tamm-Dancoff inspired approximation which is described in an earlier paper [Phys. Rev. D 58, 034003 (1998)]. The resulting system of 15 coupled non-linear differential equations self-consistently determines all quark-meson coupling constants. Also the obtained solutions for quark and meson fields are stable and physically acceptable. As the zeroth approximation of a more refined structure they were used to calculate SU(3) baryon octet magnetic moments and axial coupling constants with baryon state vectors containing valence quarks only, at this primordial level. The results are very promising, so possibilities to pursuit more sophistication and improved physical input is indicated.Received: 24 August 2004, Published online: 1 December 2004PACS: 12.39.Ba, 12.39.FeD. Horvat: dubravko.horvat@fer.hr, Correspondence to: davorh@phy.hr     

pp̄ Annihilation at rest into mesons in the quark rearrangement model and the quark annihilation modelt

pp? annihilation at rest into mesons is calculated in the quark rearrangement model in which 3 quarks and 3 antiquarks rearrange into 3 mesons and in the quark annihilation model in which one or two quark-antiquark pairs are annihilated and a quark-antiquark pair is created to form two or three mesons. The constants of the quark-meson coupling are adjusted such that the meson-nucleon interactions agree with experiment. The radial dependences of the quark-meson couplings are all assumed to be the same. This is determined by the vector-meson-quark interaction derived from the charge form factor of the proton. In the case of the decay into three mesons both rearrangement and annihilation models explain with similar reliability the branching ratio of the decay products. In the case of the decay into two-meson annihilation gives a better agreement with experiment than rearrangement.     

A Proton in the Quark-Meson Coupling Model

We investigate the structure of a proton in free space by using the quark-meson coupling model. In the model, a proton in free space is regarded as a MIT bag with σ, ω and ρ meson fields and the Coulomb potential. With the boundary condition at bag surface, the wave functions of u and d quarks and potentials are calculated self-consistently.     

The quark-meson coupling model for Λ, Σ and Ξ hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of Λ, Σ and Ξ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the Λ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, ΣN-ΛN chanel (strong conversion), is also taken into account in a phenomenological way.     

RPA method for quark-meson solitons

The quark-meson RPA equations, which describe small oscillations of a bound quark-meson system about the stationary configuration, are derived through linearization of the classical time-dependent Euler-Lagrange problem. The method has an immediate application in phenomenological quark-meson models for baryons. It provides a test of the classical stability of these systems. A number of measurable quantities, such as the spectrum of excited states and the meson-soliton phase shifts can be calculated. We demonstrate the QMRPA on a simple, 3 + 1 dimensional model of the nucleon — the chiral quark-meson model.     

Dynamics and stability of chiral fluid

Starting from the linear sigma model with constituent quarks we derive hydrodynamic equations which are coupled to the order-parameter field, e.g. the chiral fluid dynamics. For a static system in thermal equilibrium this model leads to a chiral phase transition which, depending on the choice of the quark-meson coupling constant g, could be a crossover or a first order one. We investigate the stability of the chiral fluid in the static and expanding background by considering the evolution of perturbations with respect to the mean-field solution. In the static background the spectrum of plane-wave perturbations consists of two branches, one corresponding to the sound waves and another to the σ-meson excitations. For large g these two branches cross and the excitation spectrum acquires exponentially growing modes. The stability analysis is also done for the Bjorken-like background solution by explicitly solving the time-dependent differential equation for perturbations in the η space. In this case the growth rate of unstable modes is significantly reduced.     

Phase Transitions in Neutron Stars Within Modified Quark-Meson Coupling Model

K^- condensation and quark deconfinement phase transitions in neutron stars are investigated. We use the modified quark-meson coupling model for hadronic phase and the MIT bag model for quark phase. With the equation of state （EOS） solved self-consistently, we discuss the properties of neutron stars. We find that the EOS of pure hadron matter with condensed K- phase should be ruled out by the redshift for star EX00748-676, while EOS containing unpaired quark matter phase with B1/4 being about 180 MeV could be consistent with both this observation and the best measured mass of star PSR 1913 ＋ 16. But if the recent inferred massive star among Terzan 5 with M 〉 1.68M is confirmed, all the present EOSes with condensed phase and deconfined phase would be ruled out.     

Hadron Mass and the Properties of Nuclear Matter in the Quark Bag Models

The MIT bag model, chiral bag model and cloudy bag model are revisited. A typical work on the hadron mass calculation by chiral bag model and cloudy bag model is shown in more details with the quark-quark-pi vertex correction and quark self-energy being emphasized. More details are given to review the quark-meson coupling model and its application in nuclear matter. We put forth the Lagrangian of the quark-meson coupling model and studied the possibility of using the model to calculate the hadron mass.     

The functional renormalization group and O(4) scaling

The critical behavior of the chiral quark-meson model is studied within the Functional Renormalization Group (FRG). We derive the flow equation for the scale-dependent thermodynamic potential at finite temperature and density in the presence of a symmetry-breaking external field. We perform a set of approximations to formulate and solve the FRG flow equation in the presence of fermionic degrees of freedom and test their influence on the O(4) critical properties expected in the quark-meson model. Within this scheme, the critical scaling behavior of the order parameter, its transverse and longitudinal susceptibilities as well as the correlation lengths near the chiral phase transition are computed for vanishing baryon density. We focus on the scaling properties of these observables at non-vanishing external field when approaching the critical point from the symmetric as well as from the broken phase. We confront our numerical results with the Widom–Griffiths form of the magnetic equation of state, obtained by a systematic ε expansion of the scaling function.     

Nonlinear chiral models: Soliton solutions and spatio-temporal chaos

Nonlinear effective Lagrangian models with a chiral symmetry have been used to describe strong interactions at low energy, for a long time. The Skyrme model and the chiral quark-meson model are two such models, which have soliton solutions which can be identified with the baryons. We describe the various kinds of soliton states in these nonlinear models and discuss their physical significance and uses in this review. We also study these models from the view point of classical nonlinar dynamical systems. We consider fluctuations around theB=1 soliton solutions of these models (B, being the baryon number) and solve the spherically symmetric, time-dependent systems. Numerical studies indicate that the phase space around the Skyrme soliton solution exhibits spatio-temporal chaos. It is remarkable that topological solitons signifying stability/order and spatio-temporal chaos coexist in this model. In contrast with this, the soliton of the quark-meson model is stable even for large perturbations.     

The nucleon-delta splitting in the chiral quark-meson model

Cranking techniques are employed to calculate the N − Δ splitting in the chiral quark-meson model. A splitting of 322 MeV is obtained. It is determined that about 80% of the angular momentum and isospin in the model are carried by the mesons.     

Neutron star cooling and GW170817 constraint within quark-meson coupling models

In the present work,we used five different versions of the quark-meson coupling(QMC)model to compute astrophysical quantities related to the GW170817 event and the neutron star cooling process.Two of the models are based on the original bag potential structure and three versions consider a harmonic oscillator potential to confine quarks.The bag-like models also incorporate the pasta phase used to describe the inner crust of neutron stars.With a simple method studied in the present work,we show that the pasta phase does not play a significant role.Moreover,the QMC model that satisfies the GW170817 constraints with the lowest slope of the symmetry energy exhibits a cooling profile compatible with observational data.     

A Chiral Quark-Confinement Soliton Model for one nucleon and two Nucleons

A chiral quark-meson soliton model with quark-confinement is described in the present work.This model can reasonably produce the static properties of single nucleon,nucleon-nucleon interactions and elastic scattering phase shifts.     

Strange solitons in a chiral quark-meson model

We consider aSU(3) quark soliton model based on chiral invariant quark-meson coupling. We find soliton solutions with nonzero strangeness andB=1 in the model with nontrivial kaonic fields, for values of the coupling constant greater than the phenomenologically acceptable number. Hence they do not correspond to known strange baryons.     

Effects of the density dependence of the symmetry energy on neutron stars

In this paper,we include the density dependence behavior of the symmetry energy in the improved quark mass density dependent （IQMDD） model.Under the mean field approximation,this model is applied to investigate neutron star matter and neutron stars successfully.Effects of the density dependence of the symmetry energy on neutron stars are described.     

Analysis of (1/2)+ baryon states containing fourth-family quarks from QCD sum rules

When the fourth generation of quarks have sufficiently small mixing with ordinary standard-model quarks, the hadrons made up from these quarks can be long-lived enough. We analyze the (1/2)⁺ baryon states containing fourth-generation quarks and standard-model quarks, i.e. the charm or bottom quarks, in the QCD sum rules approach. Considering the perturbative and two gluon condensate contributions in the calculation, we give the numerical results of the masses and pole residues.     

Analytic determination of the T-μ phase diagram of the chiral quark model

Using a gap equation for the pion mass a non-perturbative method is given for solving the chiral quark-meson model in the chiral limit at the lowest order in the fermion contributions encountered in a large-N _fapproximation. The location of the tricritical point is analytically determined. A mean field potential is constructed from which critical exponents can be obtained.     

Weak interaction of quarks

A theory of weak interaction of quarks is developed in the framework of SU (2) symmetry. Expressions are obtained for the probability of decay of quarks into leptoquarks, quarks into leptons, and leptoquarks into leptons. A model is also constructed of the interaction of quarks with matter in which strong and electromagnetic interactions of quarks with matter are forbidden. In this model, the weak interaction of quarks is the main form of interaction between quarks and matter. In this connection, it is suggested that quarks should be looked for in nature in the products of their weak decay in accordance with the theory developed here.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 30–36, July, 1974.     

Pion distribution amplitudes within the instanton model of QCD vacuum

The pion transition form factor for the process γ*γ* → π⁰ at spacelike values of photon momenta is calculated within the effective quark-meson model with the interaction induced by instanton exchange. The leading and next-to-leading order power asymptotics of the form factor and the relation between the light-cone pion distribution amplitudes of twists 2 and 4 and the dynamically generated quark mass are found.     

Meson hyperfine splittings and asymptotic freedom

Meson hyperfine splittings give empirical evidence that the short-ranged part of the potential binding quarks has the behavior expected of single color gluon exchange in an asymptotically free theory. Since the interaction of light confined quarks depends on only one length scale, while that of heavy confined quarks depends on two length scales, it is argued that the spin-dependent interactions are qualitatively different in the cases. Phenomenological evidence suggests that the spin-dependent interactions of light quarks are short-ranged only, while that of heavy quarks are predominantly long-ranged. It is proposed that a measurement of the F¹-F mass-difference will help clarify the nature of a possible long-ranged spin-spin interaction of strange quarks.