利用密度相关的相对论平均场理论对核物质与中子星的研究(英文)

研究和详细地比较了RMF理论中不同的有效相互作用强度的密度依赖性, 并且讨论了这种密度依赖性对于核物质和中子星性质的影响. 对于核物质, 不同的参数组给出的对称核物质的饱和点非常接近, 基本都在经验值的范围内. 对于中子星, 考虑超子后不同参数组给出的质量极限的范围为1.52—2.06 M☉, 半径为10.24—11.38 km.The density dependencies of various effective interaction strengths in the relativistic mean field and their influences on the properties of nuclear matter and neutron stars are studied and carefully compared. The differences of saturation properties given by various effective interactions are subtle in symmetric nuclear matter. The Oppenheimer Volkoff mass limits of neutron stars calculated from different equations of state are 1.52—2.06 M☉, and the radii are 10.24—11.38 km with hyperons included.     

中子星的相对论平均场研究

在相对论平均框架内计算了不同超子耦合参数下中子星内部物质的状态方程,进一步求解Oppenheimer-Volkoff方程得到了中子星的各种性质.结果表明,参数的变化对这些性质有明显的影响.     

相对论平均场研究超子星

随着引力波探测以及对中子星质量与半径的高精度测量,中子星作为超新星爆发的剩余产物正吸引着相关领域的高度关注。在中子星的内核部分,诸如超子之类的奇异自由度有可能会出现从而形成超子星。本工作在相对论平均场模型框架下研究由核子与轻子构成的中子星以及包含超子的超子星。采用目前常用的非线性相对论平均场以及密度依赖的相对论平均场参数研究了超子对超子星质量、半径、潮汐形变等性质的影响。最后讨论了介子与超子的耦合常数对超子星性质的影响,发现当矢量介子与超子耦合系数较强时,利用现有的相对论平均场模型参数可以获得大质量的超子星。     

中子星物质中的K介子凝聚

用密度相关的相对论平均场理论计算了中子星物质中的K介子凝聚,结果表明中子星物质发生K介子凝聚的临界密度约为2.75ρ₀.中子星物质URCA过程发生的临界密度在考虑DB核物质中核子自能动量修正时为ρρ0≈3.16,在不考虑DB核物质中核子自能动量修正时为ρρ0≈2.25,并进一步计算了密度相关的相对论平均场理论两种参数形式对中子星物质状态方程的影响.     

低密度物态方程对中子星性质的影响

利用相对论平均场理论描述中子星的液体区域，Fermi气体模型或者FMT，BPS,和BBP模型描述中子星外壳，分别称为Fermi gas+RMF和RMF*，计算了中子星性质并且和相对论平均场理论给出的结果进行比较. 虽然低密度物态方程对中子星最大质量、中心密度、能量密度和压强的影响很小，但是它对中子星的质量半径关系改变很大. 对应中子星的最大质量，RMF和RMF*之间的半径差别为0.23-0.33km.     

原子核结构的相对论平均场描述

简要评述近几年相对论平均场理论的发展及其在核结构研究中取得的部分进展. 主要内容包括中子晕, 质子晕, 巨晕, 激发态晕等奇特核现象, 超重核结构, 超核结构以及原子核的赝自旋对称性和反核子谱的自旋对称性等.     

基于相对论平均场有效对力的中子物质BCS-BEC渡越

基于核物质的相对论Hartree-Bogoliubov（RHB）理论,采用相对论平均场单玻色子交换形式的有效对相互作用,研究了不同对力强度下双中子关联及其中的BCS-BEC渡越现象。通过引入有效衰减因子χ调节对力强度,定量分析费米面处中子对能隙和单粒子动能比值△_Fn/e_Fn及无量纲参数1/（k_Fna）随费米动量k_Fn的演化行为,发现双中子对在χ=0.51时进入BCS-BEC渡越区域,在χ=0.67时可达到幺正极限。进而分析了中子对能隙、中子对波函数及相干长度等物理量在相应临界点处的特征,并给出渡越时双中子短程关联概率的定量判据。发现当配对中子处于平均中子间距以内的概率P（d_n）?0.80时,双中子对从纯BCS耦合过渡到BCS-BEC渡越区域。Based on the relativistic Hartree-Bogoliubov theory in nuclear matter, the dineutron correlations and the crossover from Bardeen-Cooper-Schrieffer (BCS) region of neutron Cooper pairs to Bose-Einstein condensation (BEC) are investigated with the one-boson-exchange type of pairing force generated from the relativistic mean field (RMF) model. By introducing an effective factor χ in the RMF effective pairing interaction, the density dependence of the ratios between neutron pairing gap at Fermi surface and neutron Fermi kinetic energy △_Fn/e_Fn and the dimensionless parameter 1/(k_Fna) are analyzed quantitatively. Then the criteria where dineutron correlations exactly reach the threshold of BCS-BEC crossover or unitary limit are determined to be χ=0.51 or 0.67, respectively. In addition, features of neutron pairing gap, Cooper pair wave function and dineutron coherence length are illustrated, and the value of the probability for partner neutrons correlated within the average inter-neutron distance, namely P (d_n) ?0.80, is obtained as a criterion of BCS-BEC crossover.     

中子星可观测量与不同密度段核物质状态方程的关联

中子星物质主要是由高密度非对称核物质组成.目前通过地面重离子碰撞等实验来认识高密度非对称核物质的物态还存在很大的不确定性.随着对中子星天文观测精度的提高以及可观测量的增多,基于对中子星的天文观测来反向约束高密度非对称核物质物态成为了可能.从理论上去探讨中子星的可观测量与不同密度段物态方程的关联程度,将有助于上述反向对中...     

208ΛPb的超子分布半径和中子星结构

从相对论平均场理论出发,考虑核子、超子和介子自由度,研究了208ΛPb的超子分布半径与中子星的性质以及它们之间的关系. 计算发现当超子的耦合常数比值由0.3增大到1时,对NLSH和NL3参数组,超核的超子分布半径分别由3.905和3.849fm增大到4.346和4.230fm,而中子星的最大质量分别由1.516和1.429M⊙增大到2.776和2.744M⊙,质量为1.4M⊙的中子星半径分别由13.13和12.79km增大到13.24和13.29km.即中子星的最大质量和半径随超子分布半径增大而增加. 这样只要从实验上确定208ΛPb的超子分布半径,就可以得到中子星结构的信息.     

相对论平均场理论研究原子核的磁矩

采用球形以及三轴形变的相对论平均场理论研究了满壳附近质量数A=133, 207, 209的原子核的磁矩, 分析了相对论效应以及核芯极化对磁矩的影响. 计算结果表明用包含矢量介子空间分量(奇时间分量)的三轴的相对论平均场理论 可以很好的描述满壳附近重质量区原子核¹³³Sb以及²⁰⁹Bi的磁矩.     

Neutron Star Matter Including Delta Isobars

In this paper a new phase structure of neutron star matter including nucleons and delta isobars is presented.Particle fractions populated and pion condensations in neutron star matter are investigated in this model. The existence of the pion condensations can postpone the appearance of delta isobars. We found that both the pion condensation and reduce of the ratio of delta isobar to nucleons couplings can soften the corresponding equation of state. The maximum masses and their corresponding radii of neutron stars are calculated, and the obtained values are in observational region.     

Relativistic Mean-Field Approach to Infinite Nuclear Matter and Neutron Star

The properties of infinite nuclear matter and neutron star are studied theoretically in relativistic mean-field (RMF) approach with three typical parameter sets NL1, NL-SH and TM1. It is found that all these new RMF parameter sets can very satisfactorily reproduce the properties of high density matter. Among these parameter sets, TM1, with a nonlinear ω term, reproduces a slightly smaller energy, piessure and neutron star mass than NL-SH and NL1. The ρ meson field has a large influence on the properties of neutron star and infinite nuclear matter. A detailed discussion for the significance of numerical results is also given.     

Neutron Star Matter Including Delta Isobars

In this paper a new phase structure of neutron star matter including nucleons and delta isobars is presented. Particle fractions populated and pion condensations in neutron star matter are investigated in this model. The existence of the pion condensations can postpone the appearance of delta isobars. We found that both the pion condensation and reduce of the ratio of delta isobar to nucleons couplings can soften the corresponding equation of state. The maximum masses and their corresponding radii of neutron stars are calculated, and the obtained values are in observational region.     

Isovector Scalar Field Effects in Asymmetric Nuclear Matter

Density-dependent parametrization models of the nucleon-meson coupfing constants, including the isovector scalar δ-field, are applied to asymmetric nuclear matter. The nuclear equation of state （EOS） and the neutron star properties are studied in a relativistic Lagrangian density, using the relativistic mean field （RMF） hadron theory. It is known that the δ-field in the constant coupling scheme leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses, finally influences the stability of the neutron stars. We use density-dependent models of the nucleon-meson couplings to study the properties of neutron star matter and to reexamine the （~-field effects in asymmetric nuclear matter. Our calculation shows that the stability conditions of the neutron star matter can be improved in presence of the δ-meson in the density-dependent models of the coupling constants. The EOS of nuclear matter strongly depends on the density dependence of the interactions.     

Determining Nuclear Form factor for Detection of Dark Matter in Relativistic Mean Field Theory

In this work, we derive the nuclear form factor for the spin-independent collision between the WIMPs and nucleus in terms of the relativistic mean field (RMF) theory. Comparison with the traditional form factors which are commonly used in literature is given and it is found that our results are slightly above that of the 2PF model by 4% to 8%, but deviate from the Helm form factor by 15% to 25% for the whole recoil energy spectrum of 0 ∽ 100keV. Moreover, taking Xe and Ge as examples, we show the dependenceof the form factor on the recoil energy.     

均匀强磁场中中子星物质的物态方程

在Walecka模型的平均场近似下,研究了由质子、中子和电子组成的中子星物质在均匀强磁场中的性质,发现磁场增强,物态方程会在一定程度上变硬,中子所占比例显著增加,质子和电子所占比例会显著减少,磁场对物态方程的影响比它对粒子组分的影响小.本文还分别利用流体力学公式和热力学公式分别计算了中子星物质的压强,发现磁场越强,用这两种方式计算的压强越接近,当磁场为10¹⁴T时,它们完全重合.     

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.     

超子中子星性质的温度效应

从相对论平均场理论出发,考虑核子、超子和介子的相互作用,研究了温度对中子星组成粒子、状态方程和中子星质量等的影响.发现温度越高,超子在中子星内部出现时的重子数密度越低.当密度较高时,中子星的核心区主要由超子组成,即中子星转变成以奇异粒子为主要成分的超子星,并且这种转变受到温度的影响,温度越高,转变密度越低.由于超子的出现,中子星核心高密度区域的状态方程,对于不同温度,差别不大,所以有限温度中子星的最大质量都在1.8M_⊙附近.这与观测结果相符.     

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.