核介质中强子性质的手征σ模型研究

采用手征σ模型描述核多体系统,考虑真空极化的影响,首先由核物质的饱和性质确定模型参数,进一步研究了强子性质在核介质中的变化。手征σ模型的研究结果给出,核子和ω介子的有效质量随核物质密度的增大而减小,但σ介子的有效质量随密度的增大而增大。这些结果与不满足手征对称性的Walecka模型结果进行了比较。计算中采用的重整化方法会对结果有一定的影响。The modification of hadron masses in nuclear medium is studied by using the chiral sigma model, which is extended to generate the omega meson mass by the sigma condensation in the vacuum in the same way as the nucleon mass. The chiral sigma model provides proper equilibrium properties of nuclear matter. It is shown that the effective masses of both nucleons and omega mesons decrease in nuclear medium, while the effective mass of sigma mesons increases at finite density in the chiral sigma model. The resuits obtained in the chiral sigma model are compared with those obtained in the Walecka model, which includes sigma and omega mesons in a non-chiral fashion.     

K介子协变动力学及其准粒子模型的性质

简要综述了中高能重离子碰撞中K介子的产生及研究进展。重点介绍了K介子协变动力学模型, 并在此框架内分析了中高能重离子碰撞中K+介子以及与其伴随产生的Λ超子的集体流特征。 结果表明: 协变动力学模型能够很好地给出K+介子和Λ超子的微分直接流。 相对而言, 软势给出的集体流与实验值符合更好。同时, 通过对不同输运模型中K介子准粒子模型的基本属性进行对比分析, 明确了协变动力学模型中K介子准粒子模型的质量及能量随核物质密度的变化特征, 以及周围核子的运动对于K介子基本属性的影响。In the present paper, we briefly review the progress in the study of kaon production in heavy\|ion collisions at intermediate and high energies and introduce the covariant kaon dynamics model. The collective flows of positively charged kaon and the lambda hyperon associated produced with kaon are studied in the framework of the dynamics. It shows that the directed differential flow of K+ meson and Λ hyperon can be reasonably reproduced in the covariant kaon dynamics model. The calculated results with soft equation of nuclear matter are in better agrement with experimental data. Meawhile, a detailed comparison of the properites of different quasi\|particle models in various transport model and the influence of nucleon’s movement on the effective mass and energy of the quasi\|particle in the covariant kaon dynamics model are discussed.     

核物质中△(1 232)粒子的介质效应

利用手征有效场论, 通过对核物质中核子传播子的修正, 研究了核物质中的△(1 232)粒子的有效质量和衰变宽度。 发现△(1 232)粒子的有效质量随核物质密度的增加而减小, 而衰变宽度随核物质密度的增加而增加; △(1 232)粒子衰变宽度的变化主要取决于核子有效质量以及△(1 232)粒子有效质量的变化。 Based on the chiral effective field theory (CHEFT), we study the effective mass and decay width of △(1 232) in the nuclear matter with the modified nucleon propagator. We find that the effective mass of △(1 232) decreases, while the decay width of △(1 232) increases with increasing the density of nuclear matter. And the decay width of △(1 232) mainly depends on the effective masses of nucleon and △(1 232)     

Equation of State in the σ-ω-ρ Model Supported by the Observational Data of 4U 1608-52 Neutron Star

The properties of the neutron star rotating at 619Hz （which is the spin frequency of 4U 1608-52 neutron star） are investigated by using an equation of state （EOS） of the nuclear matter in the relativistic σ-ω-ρ model. It is shown that the EOS in the relativistic σ-ω-ρ model is supported by the observational mass and radius of the 4U 1608-52 neutron star. Moreover, a
strict constraint on the polar redshift of 4U 1608-52 neutron star is obtained.     

核子-核子碰撞截面的参数化公式

核子-核子碰撞截面(σ_NN)是描述原子核反应模型中的重要物理量。 核子-核子碰撞截面包括质子-质子碰撞截面（σ_pp）、中子-中子碰撞截面（σ_NN）和中子 质子碰撞截面（σ_np）, 它们随着核子能量与核物质密度的改变而变化。人们在目前研究中提出了多种核子-核子碰撞截面关于能量和核物质密度的参数化公式,通过计算12C+12C的完全反应截面,比较了不同入射能量下使用各种核子-核子碰撞截面参数化公式对12C完全反应截面的影响。 The nucleus-nucleus cross sections(σ_NN) include the proton-proton cross section, neutron-neutron cross section, and neutron-proton cross section. σ_NN change with the variations of the incident energies and the densities. Some parameterizations of σ_NNas a function of incident energy and density have been proposed in the theoretical and experimental study of nuclear reactions. Through the calculation of reaction cross sections of 12C+12C at different energies, the effect of different σ_NN parameterizations in the reaction cross sections of 12 are studied.      

核子质量、 半径及夸克凝聚的核物质密度依赖性

简要介绍核物质中核子的质量、 半径及夸克凝聚的密度依赖关系基于QCD模型和QCD有效场论研究的现状, 并具体介绍整体色对称模型（GCM）的研究结果. GCM研究表明, 在小于临界密度的情况下, 核物质中核子的质量随核物质密度的增大而减小, 核子的半径和夸克凝聚随核物质密度的增大而增大. 当达到临界密度时, 核子质量减小为零, 核子半径变为无限大, 夸克凝聚突变为零, 进而提出一个核物质中手征对称性恢复的新机制. The status of the investigations on the nucleon mass, nucleon radius and quark condensate in the framework of QCD inspired models and QCD effective field theories is briefly reviewed. The results in the global color symmetry model (GCM) are described a little detailedly. The calculated results indicate that, before the maximal density is reached, the mass of a nucleon in nuclear matter decreases, the radius of a nucleon and the quark condensate increase very slowly, with the increase of the nuclear matter density. As the maximal nuclear matter density is reached, the mass of the nucleon vanishes gradually. The radius becomes infinite and the quark condensate vanishes suddenly. A new mechanism for the chiral symmetry restoration in nuclear matter is proposed.     

奇异强子与核子的相互作用

包含s夸克的强子称为奇异强子,它与核子相互作用的研究近年来有了长足发展 .在指出这种研究的重要意义后,从实验和理论两方面介绍奇异强子 (主要是K介子和超子 )与核子相互作用的研究现状及方法等 ,包括运动学和动力学机制、介子交换模型和夸克模型解释诸方面的问题. We try to highlight some of the key issues regarding the interactions between strange hadron and nucleon, which relate to the kinematics and dynamics mechanism, meson exchange model and quark model. Starting from a brief introduction on the main research goals, we focus on the status of experimental and theoretical investigations of kaon nucleon and hyperon nucleon interactions, which may be considered to be a necessary basis for the studies of nuclear physics with strangeness.     

Antikaon condensation in neutron star matter with strong magnetic fields

We study the influence 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 interacting through the self-consistent exchange of scalar and vector meson mean fields. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly. The results of the QMC model are compared with those obtained in a relativistic mean-field (RMF) model.     

In-medium NN→NΔ cross section and its dependence on effective Lagrange parameters in isospin-asymmetric nuclear matter

The in-medium NN→N△ cross sections and its differential cross sections in isospin asymmetric nuclear medium are investigated in the framework of the one-boson exchange model by including isovector mesons, i.e., δand p mesons. Our results show that the in-medium NN→N△ cross sections are suppressed when the density increases, and the differential cross sections become isotropic with an increase in the density around the △ threshold energy. The isospin splitting on the medium correction factor, R =σ_(NN→N△)~*/σ_(NN→N△)~(free) is observed for different channels of NN→N△, especially around the threshold energy for all the effective Lagrangian parameters. By analyzing the selected effective Lagrangian parameters, our results show that the larger effective mass is, the weaker medium correction R is.     

Antikaon Condensation and In-medium Kaon and Antikaon Production in Protoneutron Stars

Antikaon condensation and kaon and antikaon production in protoneutron stars are investigated in a chiral hadronic model （also referred to as the FST model in this paper）. The effects of neutrino trapping on protoneutron stars are analyzed systematically. It is shown that neutrino trapping makes the critical density of K^- condensation delay to higher density and fifo condensation not occur. The equation of state （EOS） of （proto）neutron star matter with neutrino trapping is stiffer than that without neutrino trapping. As a result, the maximum masses of （proto）neutron stars with neutrino trapping are larger than those without neutrino trapping. If hyperons are taken into account, antikaon does not form a condensate in （proto）neutron stars. Meanwhile, the corresponding EOS becomes much softer, and the maximum masses of （proto）neutron stars are smaller than those without hyprons. Finally, our results illustrate that the Q values for K^＋ and K^- production in （proto）neutron stars are not sensitive to neutrino trapping and inclusion of hyperons.     

Kaon and antikaon properties in cold nuclear medium

We present results of a self-consistent calculation for the kaon and antikaon spectral functions in cold nuclear matter, using as input the kaon-nucleon and antikaon-nucleon scattering amplitudes of the vacuum. We investigate the effect of in-medium pion dressing on the antikaon-nucleon scattering amplitudes and antikaon spectral function. We find the influence of pion dressing to be minor on the antikaon spectral function and limited on the hyperon resonances causing only a small additional broadening. An exception is the Σ(1690). At nuclear saturation density an attractive mass shift of about 20 MeV and width of about 130 MeV is obtained. The kaon shows a repulsive mass increase of 36 MeV and a small width of the quasiparticle peak at saturation density.     

Kaon properties in (proto-)neutron star matter

The modification of kaon and antikaon properties in the interior of (proto-)neutron stars is investigated using a chiral SU(3) model. The parameters of the model are fitted to nuclear-matter saturation properties, baryon octet vacuum masses, hyperon optical potentials and low-energy kaon-nucleon scattering lengths. We study the kaon/antikaon medium modification and explore the possibility of antikaon condensation in (proto-)neutron star matter at zero as well as finite temperature/entropy and neutrino content. The effect of hyperons on kaon and antikaon optical potentials is also investigated at different stages of the neutron star evolution.     

A Modified Pion-Rho-Omega Mesonic Lagrangian in Nuclear Matter

We present an in-medium modified effective Lagrangian which describes the pion, rho- and omega mesons and the corresponding soliton properties in nuclear matter. We discuss possible modifications of ρ- and ω-meson properties in nuclear matter. In particular, the masses of vector mesons are shown to decrease about 30% at normal nuclear matter density within the present approach.     

Influence of Self-Interaction ofσ Meson to the Equation of State of Nuclear Matter

In the relativistic σ-ωmodel, the influence of the parameters in self-interaction of a meson to the equation of state of normal nuclear matter, especially, to incompressibility, effective mass, and coupling constants, is studied in detail. We find that these parameters have an intense relationship to the property of nuclear matter. At the same time , we study the relation between the binding energy and pressure of relativestic △-resonance nuclear matter and temperature using using above results in the relativistic σ-ω-π model,and it is interesting to compare it to our prior work. In all these studies, the vacuum fluctuation on nucleon, △-isobar, and σmeson is considered.     

Antikaon production and medium effects in heavy-ion collisions at AGS

Antikaon production in heavy-ion collisions at energies available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory is studied in a relativistic transport (ART) model. We include contributions from the baryon-baryon, meson-baryon, and meson-meson interactions. The final-state interaction of antikaons via both absorption and elastic scattering by nucleons and pions are also considered. To compare with presently available or future experimental data, we have calculated the antikaon rapidity and transverse momentum distributions as well as its collective flow. Medium effects on these observables due to mean field potentials have also been investigated. It is found that both the ratio of antikaon transverse momentum spectrum to that of kaon and their transverse flow are most sensitive to the in-medium properties of kaons and antikaons.     

The study of the binding energy of nuclear matter in the relativistic σ− ω− π model with Δ isobar degree of freedom

The relativistic σ?ω?π model is proposed and used to calculate the binding energy of relativistic nuclear matter. By coupling Δ isobar to the σ meson, the zero-point fluctuation energy of the Δ isobar in the one loop approximation is derived. We calculate the effective mass of nucleon and Δ isobar, exchange and correlation energies, pressure and incompressibility of nuclear matter. The density dependence correction to σNN ωNN coupling constants is a very important mechanism to saturate the binding energy. The pion propagator is nuclear matter is constructed by the relativistic particle-hole, delta-hole and short-range correlation. The pion dispersion relation is calculated we find it’s very sensitive to the effective mass of nucleon and Δ isobar.     

核物质中内介质等效手征Lagrange量和π介子质量

在核物质中从手征等效Lagrange量得到的π介子有效质量是单值的,并且与π介子场的离壳扩展无关,例如PCAC选择.同位旋对称核物质中的有效π介子质量随增加的核密度有些上升,因此有效类时π介子衰变常数和密度相关的夸克凝聚渐渐下降.另外研究了内介质Gell–Mann–Oakes–Renner关系和其它内介质同一性.最后讨论了同位旋对称、各向同性和均匀的核物质中关于介子传播的等效Lagrange量的几个限制.     

The high-density symmetry energy in heavy ion collisions

The nuclear symmetry energy as a function of density is rather poorly constrained theoretically and experimentally both below saturation density, but particularly at high density, where very few relevant experimental data exist. We discuss observables which could yield information on this question, in particular, proton-neutron flow differences, and the production of pions and kaons in relativistic heavy ion collisions. For the meson production we investigate particularly ratios of the corresponding isospin partners π⁻/π⁺ and K⁰/K⁺, where we find that the kaons are an interesting probe to the symmetry energy. In this case we also discuss the influence of various choices for the kaon potentials or in-medium effective masses.     

Antikaon production in nucleon- nucleon reactions near threshold

The antikaon production cross section from nucleon-nucleon reactions near threshold is studied in a meson exchange model. We include both pion and kaon exchange, but neglect the interference between the amplitudes. In case of pion exchange the antikaon production cross section can be expressed in terms of the antikaon production cross section from a pion-nucleon interaction, which we take from the experimental data if available. Otherwise, a K* -resonance exchange model is introduced to relate the different reaction cross sections. In case of kaon exchange the antikaon production cross section is related to the elastic KN and K?N cross sections, which are again taken from experimental measurements. We find that the one-meson exchange model gives a satisfactory fit to the available data for the NN → NN KK? cross section at high energies. We compare our predictions for the cross section near threshold with an earlier empirical parameterization and that from phase space models.