核物质和夸克物质的对称能（英文）

对称能表征了同位旋非对称强相互作用物质状态方程的同位旋相关部分,它对于理解核物理和天体物理中的许多问题有重要意义。简要总结了关于核物质和夸克物质对称能研究的最新进展。对于核物质对称能,通过对核结构,核反应以及中子星的研究,目前对其亚饱和密度的行为已有比较清楚的认识,同时,对饱和密度附近对称能的约束也取得了很好的研究进展。但如何确定核物质对称能的高密行为仍然是一个挑战。另一方面,在极端高重子数密度条件下,强相互作用物质将以退禁闭的夸克物质状态存在。同位旋非对称夸克物质可能存在于致密星内部,也可能产生于极端相对论重离子碰撞中。对最近关于夸克物质对称能对夸克星性质的影响以及重夸克星的存在对夸克物质对称能的约束的研究工作进行了介绍,结果表明同位旋非对称夸克物质中上夸克和下夸克可能感受到很不一样的相互作用,这对于研究极端相对论重离子碰撞中部分子动力学的同位旋效应有重要启发。The symmetry energy characterizes the isospin dependent part of the equation of state of isospin asymmetric strong interaction matter and it plays a critical role in many issues of nuclear physics and astrophysics. In this talk, we briefly review the current status on the determination of the symmetry energy in nucleon (nuclear) and quark matter. For nuclear matter, while the subsaturation density behaviors of the symmetry energy are relatively well-determined and significant progress has been made on the symmetry energy around saturation density, the determination of the suprasaturation density behaviors of the symmetry energy remains a big challenge. For quark matter, which is expected to appear in dense matter at high baryon densities, we briefly review the recent work about the effects of quark matter symmetry energy on the properties of quark stars and the constraint of possible existence of heavy quark stars on quark matter symmetry energy. The results indicate that the u and d quarks could feel very different interactions in isospin asymmetric quark matter, which may have important implications on the isospin effects of partonic dynamics in relativistic heavy-ion collisions.     

手征胶子修正夸克平均场模型

这项工作利用考虑π介子与胶子效应的夸克平均场模型研究原子核结构的基本性质。在夸克平均场中,核子由三个束缚在谐振子势场中的组分夸克构成。描述强相互作用的量子色动力学必须满足手征对称性,此外夸克之间也需要通过交换胶子相互作用。因此,在夸克平均场模型中,对利用夸克势获得的核子质量考虑π介子修正与胶子修正。通过少数稳定有限核的结合能与半径实验值确定模型中的未知参数,获得了一组夸克平均场相互作用参数,QMF-NK。利用该组参数计算40Ca和208Pb的电荷密度分布,发现与实验值符合很好。随后获得了与经验值一致的对称核物质的饱和性质。包含π介子修正和胶子修正的夸克平均场模型能够更好地描述有限核和核物质的性质。The basic properties of nuclear structure are studied within the quark mean field (QMF) model by taking the effects of pions and gluons into account. In QMF, the nucleon is made up of three constituent quarks confined by a harmonic oscillator potential. The quantum chromodynamics describing the strong interaction must satisfy the chiral symmetry and quarks interact with each other through exchange of gluons. Therefore pion correction and gluon correction are included in the nucleon mass obtained by using quark confinement potential in quark mean field model. We determine the unknown parameters in the model by fitting the experimental data of the binding energies and radii of several stable finite nuclei and obtain a set of parameters of quark mean field interaction, named QMF-NK. The charge density distributions of 40Ca and 208Pb are calculated, which are in good agreement with the experimental data. Later the saturation properties of symmetric nuclear matter which are consistent with the empirical data are obtained. With the pion and gluon corrections, the QMF model could treat finite nuclei and nuclear matter better.     

核子自旋结构

简要介绍了夸克的发现、核子的夸克模型 ,详细讨论了夸克模型中核子内夸克自旋结构和极化轻子-核子深度非弹散射测量出的夸克自旋结构中的矛盾 .指出这个矛盾是由于对夸克自旋理解的混淆.最后还讨论了规范不变性和正则量子化两大物理学原则在夸克、电子轨道角动量上出现的矛盾. A simple introduction of the discovery of quark and the constituent quark model of nucleon have been given. The contradiction between the quark spin structure of nucleon of the constituent quark model and the measured one in the polarized deep inelastic lepton nucleon scattering has been explained in detail. It is elucidated that the so called “proton spin crisis” is due to quark spin confusion. The incompatibility between the requirement of gauge invariance and ...     

Some Properties of π Meson in Nuclear Matter with Finite Density

In the GCM we study some properties of π meson as the Goldstone bosons in a nuclear matter with finite density.Using the effective action in a nuclear matter,we calculate the decay constant and π mass as functions of the chemical potential.The relation between the chemical potential and the density of a nuclear matter is firstly given here.We find that fπ and mπ monotonously decrease as nuclear matter density increases.The result is consistent with the usual assumption that the chiral symmetry is gradually restored as the density of a nuclear matter increases.     

Nucleon excitations

The mass pattern of nucleon and Δ resonances is compared with predictions based on quark models,the Skyrme model,AdS/QCD,and the conjecture of chiral symmetry restoration.     

Finite Size Effect on the in-Medium Chiral Condensate at Finite Density

The in-medium quark condensate is studied with an equivalent quark mass approach that has the advantage of no need for extra assumptions on the current mass derivatives of model parameters with respect to the quark current mass. It is found that the ratio of the quark condensate in a medium to that in a vacuum depends not only on density but also on the finite size. With decreasing volume, it decreases to a minimum, and then saturates at a radius of about 1 fro. The condensate approaches to its bulk value when the volume becomes infinitely large, and it decreases finearly with increasing density if the density is extremely low.     

Quark Condensate in the Strange Matter

In a nonlinear chiral SU(3) framework, we investigate the quark condensate in the strange matter including N, Σ, Ξ, and Λ, making use of chiral symmetry spontaneous breaking Lagrangian and mean-field approximation. The results show that the chiral symmetry is restored partially when the strange matter density increases and that 〈π→2〉 plays a very important role in the strange matter which may approach the constituents of the neutron stars. In addition, we can find that the strange matter density where the π-condensate emerges leads to the ratio of the nucleon number to baryon number.     

夸克的横向性分布与核子张量荷

夸克的横向性分布的一次矩定义了核子张量荷. 核子张量荷也可用张量流算符在核子态的矩阵元定义,由此用量子色动力学求和规则、有效理论和模型计算了核子张量荷. 对研究核子性质及强子物理的自洽非微扰途径问题也作了简要讨论. The first moment of quark transversity distribution defines the tensor charge of nucleon. The tensor charge of nucleon can also be defined as the forward matrix element of the tensor current in the nucleon state，which is used to study the nucleon’s tensor charge in terms of quantum color dynamics(QCD) sum rule approach， the effective theory and model. A consistent nonperturbative approach to study nucleon property and hadronic physics is also discussed.     

Nucleon excitations

The mass pattern of nucleon and Δ resonances is compared with predictions based on quark models,the Skyrme model,AdS/QCD,and the conjecture of chiral symmetry restoration.     

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)     

Density dependence of nucleon radius and mass in the global color symmetry model of QCD with a sophisticated effective gluon propagator

Making use of the global color symmetry model (GCM) at finite chemical potential and with a sophisticated effective gluon propagator, the density dependence of the bag constant, the total energy and the radius of a nucleon in nuclear matter is investigated. A maximal nuclear matter density for the existence of the bag with three quarks confined within is given as about 8 times the normal nuclear matter density. The calculated results indicate that, before the maximal density is reached, the bag constant and the total energy of a nucleon decrease, and the radius of a nucleon increases, with the increasing of the nuclear matter density. As the maximal nuclear matter density is reached, the mass and the bag constant of the nucleon vanish and the radius becomes infinite suddenly. It manifests that a phase transition from nucleons to quarks takes place. Meanwhile, shortening the interaction range among quarks can induce the phase transition to happen easier.     

Quark Mass Dependence of Nucleon Magnetic Moment and Charge Radii

Understanding hadron structure within the framework of QCD is an extremely challenging problem. Our purpose here is to explain the model-independent consequences of the approximated chiral symmetry of QCD for two famous results concerning the quark structure of the nucleon. We show that both the apparent success of the constituent quark model in reproducing the ratio of proton to neutron magnetic moments and the apparent success of the Foldy term in reproducing the observed charge radius of the neutron are coincidental. That is, a relatively small change of the current quark mass would spoil both results.     

Quark Mass Dependence of Nucleon Magnetic Moment and Charge Radii

Understanding hadron structure within the framework of QCD is an extremely challenging problem. Our purpose here is to explain the model-independent consequences of the approximated chiral symmetry of QCD for two famous results concerning the quark structure of the nucleon. We show that both the apparent success of the constituent quark model in reproducing the ratio of proton to neutron magnetic moments and the apparent success of the Foldy term in reproducing the observed charge radius of the neutron are coincidental. That is, a relatively small change of the current quark mass would spoil both results.     

利用非对称核物质状态方程对中子星的质量和半径的研究

在温度、密度及同位旋相关的核物质状态方程的基础上,通过求解Tol-man-Oppenheimer?Volkoff方程得到了中子星的质量与中心密度的关系,发现随着中心密度的变化,中子星存在一个最大质量.同时计算结果表明,中子星的最大质量与核物质状态方程的不可压缩系数、有效质量及对称能强度系数等密切相关.对中子星半径的研究表明,较硬的核物质状态方程给出的中子星半径较大,而且较大的对称能强度系数和较大的核子有效质量也会给出较大的中子星半径.     

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.     

Modified Quark-Meson-Coupling Model and Quark Condensate in Nuclear Matter

The in-medium quark condensates will decrease as the density of nuclear matter increases if the original QMC model has been modified by introducing the u-dependent couplings, and this modification will lead to in-medium quark condensates completely vanished at about three times the saturation density of nuclear matter. This result is consistent with that of the model-independent approximation. Then, the effects of the empirical nucleon radii on the quark condensates are. calculated systematically.     

Calculation of Quark Condensate in Nuclear Matter with the Chiral Symmetry Spontaneous Breaking Lagrangian

Using the chiral symmetry spontaneous breaking Lagrangian with mean-field approximation, we investigate the in-medium quark condensate 〈qq〉. It is found that the condensate decreases as the nuclear matter density ρ increases. Meanwhile, the desent deviates from the linear decrease and becomes remarkably slow as the density of the nuclear matter further increases. It shows that the chiral symmetry spontaneous breaking is only partially restored in densed nuclear matter.     

Properties of the nucleon in the nuclear medium within a chiral quark-meson theory

The modifications of the nucleon structure due to the presence of an external baryon medium are investigated in a chiral quark meson theory. To that end the Nambu-Jona-Lasinio (NJL) model is combined with the projected chiral soliton model. The medium effects are incorporated using the medium modified values of the pion decay constant and the pion and sigma masses at finite density. These values are evaluated within the NJL model. Using functional integral techniques the latter is solved in a quark continuum at finite density. The effective meson values serve to fix the parameters of the linear chiral sigma model which is solved in a variational projected mean field approach in order to obtain the nucleon properties. All nucleon properties show modifications in the medium except for the pion nucleon coupling constant. The proton radius shows an increase of 19% and the nucleon mass a decrease of 17% if the medium reaches nuclear matter density. The magnetic moments and axial vector coupling constant are less modified. All form factors show remarkable reduction at finite transfer momenta.