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.     

Deformed even-even nuclei in a quark-meson coupling model with tensor coupling

Neutron total cross sections of ¹⁹⁷Au and ^natTa have been measured at the nELBE photoneutron source in the energy range 0.1–10MeV with a statistical uncertainty of up to 2% and a total systematic uncertainty of 1%. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5ps) with a short flight path of 7m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources.     

Critical analysis of quark-meson coupling models for nuclear matter and finite nuclei

Three versions of the quark-meson coupling (QMC) model are applied to describe properties of nuclear matter and finite nuclei. The models differ in the treatment of the bag constant and in terms of non-linear scalar self-interactions. In two versions of the model the bag constant is held fixed at its free-space value whereas in the third model it depends on the density of the nuclear environment. As a consequence opposite predictions for the medium modifications of the internal nucleon structure arise. After calibrating the model parameters at equilibrium nuclear matter density, binding energies, charge radii, single-particle spectra and density distributions of spherical nuclei are analyzed and compared with QHD calculations. For the models which predict a decreasing size of the nucleon in the nuclear environment, unrealistic features of the nuclear shapes arise.     

Effect of momentum anisotropy on quark matter in the quark-meson model

We investigate the chiral phase structure of quark matter with spheroidal momentum-space anisotropy specified by one anisotropy parameter ξ in the 2+1 flavor quark-meson model.We find that the chiral phase diagram and the location of the critical endpoint(CEP) are significantly affected by the value of ξ.With an increase inξ,the CEP is shifted to lower temperatures and higher quark chemical potentials.In addition,the temperature of the CEP is more sensitive to the anisotropy parameter than the corresponding quark chemical potential,which is the opposite to that from the finite system volume effect.The effects of the momentum anisotropy on the thermodynamic properties and scalar(pseudoscalar) meson masses are also studied at the vanishing quark chemical potential.The numerical results reveal that an increase in ξ can hinder the restoration of chiral symmetry.We also find that shear viscosity and electrical conductivity decrease as ξ increases.However,the bulk viscosity exhibits a significant nontrivial behavior with ξ in the entire temperature domain of interest.     

Medium dependence of the bag constant in the quark-meson coupling model

Possible variations of the quark-meson coupling (QMC) model are examined in which the bag constant decreases in the nuclear medium. The reduction is supposed to depend on either the mean scalar field or the effective mass of the nucleon. It is shown that the electric and magnetic radii of the bound nucleon are almost linearly correlated with the bag constant. Using the fact that the size of the bound nucleon inside a nucleus is strongly constrained by y-scaling data in quasi-elastic, electron-nucleus scattering, we set a limit for the reduction allowed in the bag constant for these two models. The present study implies that the bag constant can decrease up to 10–17% at average nuclear density, depending on the details of the model.     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<M_cr could survive the early stages of their evolution without decaying to a quark star.     

Phase transitions in hadronic matter

We formulate an equation of state for strongly interacting matter, which leads to a phase transition from massive resonance excitation to ideal gas behaviour. The structural similarity to the Van der Waals equation is discussed, as are extensions to describe hadron to quark matter transitions.     

Statistical bootstrap model and critical behaviour of hadronic matter

The critical behaviour of two different macroscopic hadron systems is studied, using a linearly exponential mass spectrum:p≈-m ^a exp(bm). It is shown that near the critical point, fora相似文献   

String dynamics in hadronic matter

Hadron production in soft hadronic collisions is successfully described by a longitudinal excitation and subsequent decay of color flux tubes. We consider the dynamics of interacting unstable strings as a generalization designed forhA andAA interactions at ultrarelativistic energies. The constituent quarks at the ends of the decaying strings and the produced hadrons can interact with the surrounding matter. The effect of secondary interactions in molecular dynamics calculations forAA collisions at CERN energies (200A GeV) can be seen in an enhancement of transverse energy, particle production and the mean transverse momenta. The results agree very well with the experimental measurements at ultrarelativistic beam energies inpp, hA and the recentAA collisions.     

Kaon production in hadronic matter

Subthreshold kaon production has been studied in symmetric nucleus-nucleus collisions as a function of the nucleus mass, beam energy and centrality. In Au+Au collsions at 1 AGeV theK ⁺ multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce the data. The in-mediumK ^? cross section measured in Ni+Ni collisions is enhanced by about a factor of 7 as compared to the free cross section when using theK ⁺ cross section at equivalent beam energies as a normalization.     

Neutron star matter in a modified PNJL model

We discuss a three-flavor Nambu-Jona-Lasinio model for the quark matter equation of state with scalar diquark interaction, isoscalar vector interaction and Kobayashi-Maskawa-??t Hooft interaction. We adopt a phenomenological scheme to include possible effects of a change in the gluon pressure at finite baryon density by including a parametric dependence of the Polyakov-loop potential on the chemical potential. We discuss the results for the mass-radius relationships for hybrid neutron stars constructed on the basis of our model EoS in the context of the constraint from the recently measured mass of (1.97 ± 0.04) M _?? for the pulsar PSR J1614-2230.     

Chiral-symmetry restoration in clustered hadronic matter

Chiral-symmetry restoration is usually discussed in the context of quark matter, a system of deconfined quarks. However, many systems like stable nuclei and neutron stars have quarks confined within nucleons. In the present paper we use a Fermi sea of three-quark clusters instead of a Fermi sea of deconfined quarks to investigate the in-medium quark condensate. We find that an enhancement of the chiral breaking in clustered matter as claimed in the literature is not a consequence of the clustering but rather dependent on the microscopic model dynamics.Received: 30 September 2002, Published online: 22 October 2003PACS: 21.65. + f Nuclear matter - 24.85. + p Quarks, gluons, and QCD in nuclei and nuclear processes - 12.39.-x Phenomenological quark models     

The speed of sound in hadronic matter

We calculate the speed of sound c _s in an ideal gas of resonances, whose mass spectrum is assumed to have the Hagedorn form ρ(m)～m ^?a exp?{bm}, which leads to singular behavior at the critical temperature T _c =1/b. With a=4 the pressure and the energy density remain finite at T _c , while the specific heat diverges there. As a function of the temperature, the corresponding speed of sound initially increases similarly to that of an ideal pion gas, until near T _c resonance effects dominate, which causes c _s to vanish as (T _c ?T)^1/4. In order to compare this result to the physical resonance gas models, we introduce an upper cut-off M in the resonance mass integration. Although the truncated form still decreases somewhat in the region around T _c , the actual critical behavior in these models is no longer present.