对称能研究进展(英文)

总结了目前基于分析地面实验室以及天文观测数据所得到的关于核物质对称能密度相关性的约束。结果表明,在核物质饱和密度ρ0处,关于对称能的大小Esym(ρ0)及其密度梯度参数L的不同具体约束强烈地依赖于不同的实验数据或理论方法。另一方面,所有存在的约束都和Esym(ρ0)=(32.5±2.5)MeV以及L=(55±25)MeV一致。如何确定核物质对称能的高密行为仍然是一个挑战。     

核物质对称能斜率对快转中子星性质的约束（英文）

在过去的十余年中,对非对称核物质的对称能的研究无论从实验还是理论上都取得了较大的突破,这对中子结构及其物态方程的理解具有十分重要的意义。本研究将采用一个相对保守的对称能斜率范围(25 Me VL105Me V)来研究其对快速转动中子星性质的约束,这些性质包括:质量-半径关系、转动惯量、引力红移以及转动形变等。通过该对称能斜率的约束,发现典型中子星(M=1.4M⊙)的半径约束在10.28～13.43 km范围内,这与最近的相关观测相一致。如果观察发现了质量较小的毫秒脉冲星,则将为核物质的对称能较软提供有效的证据。另外还发现,对角动量的一致性可为快转中子星转动惯量的上限提供约束。最后,根据具有低质量伴星的双星EXO0748-676的红移观测,给出了该脉冲星的质量下限(1.5M⊙)。     

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.     

核物质对称能的高密行为研究

同位旋物理的主要任务之一是通过放射性核束引起的核反应来探索介质中有效核子-核子相互作用的同位旋依赖性,尤其是同位旋相关的核物质状态方程, 即密度依赖的核物质对称能。由于对称能,尤其是其高密行为,对核物理学和天体物理学具有重要意义,密度依赖的对称能在过去10年一直是中能重离子物理研究领域的主要焦点之一。近年来,低密对称能的研究已经取得了重要进展, 而对称能的高密行为仍然很不确定。在理论方面,人们提出了许多对高密对称能敏感的观测量。 实验方面, 关于对称能高密行为研究的实验计划已经展开,世界各地正在建造的放射性核束装置为对称能的高密行为研究提供了新的机遇。基于IBUU输运模型综述了研究对称能高密行为的一些敏感观测量及其最新进展, 以及所面临的挑战与机遇。One of the major tasks of studying isospin physics via heavy ion collisions with neutron rich nuclei, is to explore the isospin dependence of in medium nuclear effective interactions and the equation of state of neutron rich nuclear matter, i.e., the density dependence of nuclear symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of nuclear symmetry energy has been the main focus of the intermediate energy heavy ion physics community during the last decade. Nowadays significant progress has been achieved in studying the low density behavior of nuclear symmetry energy, but the high density behavior of nuclear symmetry energy is still very uncertain. Theoretically, a number of observables have been proposed as sensitive probes to the high density behavior of nuclear symmetry energy. With new opportunities provided by the various radioactive beam facilities being constructed around the world, studies of the high density behavior of nuclear symmetry energy is expected to be one of the main forefront research areas in nuclear physics in the near future. In this report, based on the transport model IBUU we have reviewed the major progress achieved in studying the high density behavior of nuclear symmetry energy and discussed future challenges in this field.     

低温核物质的性质与可能的夸克机制

本文用夸克袋模型来描述核子,并设核子内的夸克与标量和矢量介子场相耦合,考虑核子在核物质中的费米运动,计算了核物质内核子内禀特性随系统密度和温度的变化,给出了不同温度下单核子束缚能的变化曲线.     

核物质中的夸克凝聚

核物质中的夸克凝聚是在夸克层次研究核物理遇到的基本问题之一,特别是,它与核环境下强子性质的研究紧密相关．近年来,国内外对此开展了若干研究．简要介绍这方面的研究现状和指出存在的问题． Quark condensates in nuclear matter are one of the key problems for the study of nuclear physics at quark lever, and it is related closely to a deeper understanding of the properties of hadrons in nuclear matter. Recently we have seen some investigations made of the above subject. The present status and open problems are described in this paper.     

核物质对称能和对称自由能的温度相关性

基于同位旋和动量相关的MDI相互作用, 研究了核物质对称能和对称自由能的温度相关性. 利用得到的密度和温度相关的对称能, 分析了同位旋标度实验的数据.     

同位旋非对称核物质性质与扩展的BHF方法(Ⅱ)状态方程、对称能以及三体核力效应

在同位旋相关的BHF理论框架内,研究了微观三体核力对非对称核物质状态方程和原子核对称能的影响.结果表明:即使引进了微观三体核力后,核物质结合能随同位旋非对称度的变化关系仍然能够在整个同位旋自由度范围内(0≤β≤1)相当精确地满足二次方规律.在核物质饱和密度ρ₀=0.17fm^－3处,三体核力对于对称能E_sym的影响很小,考虑三体核力后得到的对称能为30.71MeV,与其经验值符合得很好;对于高密度核物质,由于三体核力效应,对称能明显增大,而且三体核力使对称能随密度的增大要比不考虑三体核力情况下的计算结果陡得多.同时还给出了对称能的密度依赖关系的一个简单的参数化形式.     

自旋极化的对称核物质和中子物质的性质

利用Skyrme有效相互作用对自旋极化的同位旋对称核物质和中子物质的特性进行了研究.用4种核子-核子相互作用参数SⅢ,SKM,SLy230a和SLy230b,分别描绘了核物质状态方程曲线.可以发现不论使用哪一种参数,在自旋极化的同位旋对称核物质和中子物质中都存在着磁化相变转换点.另外还对磁化系数进行了计算,给出了磁化系数比率随密度的变化关系,由于无限不连续点的存在,进一步肯定了在Skyrme-Hartree-Fock理论框架内两种物质会出现磁化相变转换点.     

原子核对称能对中子星壳层结构的影响

中子星内壳层中存在原子核、中子、电子等非均匀分布的物质。在Wigner-Seitz近似下,共存相方法和自洽Thomas-Fermi近似方法是描述这种非均匀物质的有效方法。中子在非均匀物质所占的比例远远大于其他组分,因此原子核的对称能对非均匀物质的性质会产生十分重要的影响,而原子核对称能的密度依赖关系在核物质饱和密度附近有较大的不确定性。采用相对论平均场理论描述核子间相互作用,研究原子核对称能对中子星内壳层的密度范围、pasta相结构、壳核相变密度等性质的影响,探寻其中可能存在的关联。计算结果表明,原子核对称能及其密度依赖性在决定中子星内壳层非均匀物质的性质中起着重要作用,这与之前相关研究中得到的结论基本相符。Within Wigner-Seitz approximation, both the coexisting phases method and the self-consistent Thomas-Fermi approximation can be used to describe the nonuniform matter consisting of nuclei, neutrons, and electrons, which may coexist in the inner crust of neutron star. Since the neutron fraction is very large, nuclear symmetry energy may have an important impact on the properties of nonuniform matter. However, the density dependence of nuclear symmetry energy around saturation density is still rather uncertain. This paper focuses on the influence of nuclear symmetry energy on the density range of inner crust, pasta phase structure, and crust-core transition density of neutron star, where the relativistic mean field theory is adopted to describe the nucleon-nucleon interaction. It is turned out that the nuclear symmetry energy and its density dependence play an import role in determining the properties of nonuniform matter in the inner crust of neutron star, which is consistent with the former related studies.     

核物质的对称能与中子皮厚度(英文)

在现有的平均场模型中引入同位旋相关的高阶修正项．研究了核物质对称能的密度依赖性和。^208Pb的中子皮厚度。采用新提出的PK1相互作用以及NL3．S271和Z271相互作用．得到核物质饱和点对称能的范围为29-38MeV以及相应的^208Pb中子皮厚度为0．17—0.28fm．在所有相互作用中，核物质饱和点的对称能与^208Pb的中子皮厚度近似呈线性关系。After adding isospin dependent high order correction terms to existing relativistic mean field models (RMF), the density dependence of symmetry energy and the neutron skin thickness S for 208Pb are studied. Using the new effective interaction PK1, together with NL3, S271 and Z271, a range of 29—38 MeV for the symmetry energy for nuclear matter at saturation point and the corresponding neutron skin thickness S = 0.14—0.28 fm for 208Pb are obtained. For all effective interactions, a linear relation between the symmetry energy at saturation point and the neutron skin thickness for 208Pb is observed.     

Nuclear Matter in a Chiral SU(3) Quark Mean-Field Model

A quark meson coupling model based on SU(3)_L×SU(3)_R symmetry and scale invariance is proposed. The quarks and mesons get masses through symmetry broken. We apply this SU(3) chiral constituent quark model to investigating the nuclear matter at finite temperature and density. The effective baryon masses, compression modulus and hyperon potentials are all reasonable. The critical temperature of liquid-gas phase transition is also calculated in this model.     

Constraints on Non-Radial Oscillation Modes by Symmetry Energy Slope

The effect of the nuclear symmetry energy slope on the non-radial oscillation f-modes in neutron stars is calculated and discussed. Based on a conservative range of the symmetry energy slope constrained by the experiment and theoretical analysis, a constraint on the frequency and damping time of the gravitational radiation from the f-mode in neutron star is obtained. It is also shown that a higher symmetry energy slope corresponds with a smaller frequency and a longer damping time. Meanwhile, a new set of parameters is given to present the universal properties of the scaled frequency and damping time.     

Nucleon Finite Volume Effect and Nuclear Matter Properties in a Relativistic Mean-Field Theory

Effects of excluded volume of nucleons on nuclear matter are studied, and the nuclear properties that follow from different relativistic mean-field model parametrizations are compared. We show that, for all tested parametrizations,the resulting volume energy a1 and the symmetry energy J are around the acceptable values of 16 MeV and 30 MeV,and the density symmetry L is around 100 Me V. On the other hand, models that consider only linear terms lead to incompressibility K0 much higher than expected. For most parameter sets there exists a critical point (ρc,δc), where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero. This critical point depends on the excluded volume parameter r. If this parameter is larger than 0.5 fm, there is no critical point and the pure neutron matter is predicted to be bound. The maximum value for neutron star mass is 1.85M⊙, which is in agreement with the mass of the heaviest observed neutron star 4U0900-40 and corresponds to r = 0.72 fm. We also show that the light neutron star mass (1.2M⊙) is obtained for r (≌) 0.9 fm.     

Nucleon Finite Volume Effect and Nuclear Matter Properties in a Relativistic Mean-Field Theory

Effects of excluded volume of nucleons on nuclear matter are studied, and the nuclear properties that follow from different relativistic mean-field model parametrizations are compared. We show that, for all tested parametrizations, the resulting volume energy al and the symmetry energy J are around the acceptable values of 16 MeV and 30 MeV, and the density symmetry L is around 100 MeV. On the other hand, models that consider only linear terms lead to incompressibility Ko much higher than expected. For most parameter sets there exists a critical point （pc, δc）, where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero. This critical point depends on the excluded volume parameter r. If this parameter is larger than 0.5 fm, there is no critical point and the pure neutron matter is predicted to be bound. The maximum value for neutron star mass is 1.85M⊙, which is in agreement with the mass of the heaviest observed neutron star 4U0900-40 and corresponds to r = 0.72 fm. We also show that the light neutron star mass （1.2M⊙） is obtained for r ≌ 0.9 fro.