Neutron stars with isovector scalar correlations

Neutron stars with the isovector scalar δ-field are studied in the framework of the relativistic mean-field (RMF) approach in a pure-nucleon-plus-lepton scheme. The δ-field leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses. Both features are influencing the stability conditions of the neutron stars. Two parametrizations for the effective nonlinear Lagrangian density are used to calculate the nuclear equation of state (EOS) and the neutron star properties, and compared to correlated Dirac-Brueckner results. We conclude that in order to reproduce reasonable nuclear structure and neutron star properties within a RMF approach, a density dependence of the coupling constants is required.     

Relativistic equation of state of nuclear matter for supernova and neutron star

We construct the equation of state (EOS) of nuclear matter using the relativistic mean field (RMF) theory in the wide density, temperature range with various proton fractions for the use of supernova simulation and the neutron star calculations. We first construct the EOS of homogeneous nuclear matter. We use then the Thomas-Fermi approximation to describe inhomogeneous matter, where heavy nuclei are formed together with free nucleon gas. We discuss the results on free energy, pressure and entropy in the wide range of astrophysical interest. As an example, we apply the resulting EOS on the neutron star properties by using the Oppenheimer-Volkoff equation.     

Hadron masses in medium and neutron star properties

We investigate the properties of the neutron star with relativistic mean-field models. We incorporate in the quantum hadrodynamics and in the quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is obtained and is employed in Oppenheimer-Volkov equation to extract the maximum mass of the stable neutron star. We find that the equation of state, the composition and the properties of the neutron stars are sensitive to the values of the meson masses in medium.     

致密物质性质和适用于超新星及中子星研究的状态方程(英文)

采用相对论平均场方法研究了致密物质的性质, 构造了包括较宽温度、 同位旋不对称度和密度范围的适用于超新星模拟研究的状态方程, 均匀物质由相对论平均场理论描述, 非均匀物质由托马斯 费米近似给出。讨论了包含超子自由度的中子星物质的状态方程。 计算结果表明, 包含超子可以有效地软化高密度区的状态方程, Λ超子的超流态有可能存在于大质量中子星内部。The properties of dense matter are studied within the relativistic mean field theory. The equation of state (EOS) of dense matter are constructed covering a wide range of temperature, proton fraction, and density for the use of supernova simulations. The relativistic mean field theory is employed to describe the uniform matter, while the Thomas Fermi approximation is adopted to describe the non uniform matter. The EOS of neutron star matter is discussed with the inclusion of hyperons. It is found that the EOS at high density can be significantly softened by the inclusion of hyperons. The 1S₀ superfluidity of Λ hyperons may exist in massive neutron stars.     

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the proton-neutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron-rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density-dependent relativistic mean-field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.     

The Effect of Hyperon-Hyperon Interaction on Neutron Stars

The equations ofstate of the neutron star matter are calculated in the relativistic mean-field approximation witl different hyperon coupling constants. The properties of neutron stars are studied by solving the OppenheimerVolkoff equation. It manifests the properties of neutron stars - change explicitly as different hyperon coupling constants are concerned.``     

Study of the Binding Energy of Relativistic Nuclear Matter in the Relativistic σ-ω-π Model

A relativistic σ-ω-π model is proposed to calculate the binding energy of relativistic nuclear matter. We put emphasis on the relativistic particle-hole, delta-hole excitation of pion propagator in nuclear matter. The renormalization of the nucleon self-energy in nuclear matter is made for the pseudo-vector πNN and πNΔ couplings by introducing corresponding form factor and by dispersion relation. We find that the density dependence correction to meson-NN coupling constants is very important to saturate the binding energy of nuclear matter. The density dependence correction to πNN and πNΔ coupling constants has the effect of softening the EOS of nuclear matter.     

The Effect of Hyperon-Hyperon Interaction on Neutron Stars

The equations of state of the neutron star matter are calculated in the relativistic mean-field approximation with different hyperon coupling constants. The properties of neutron stars are studied by solving the Oppenheimer-Volkoff equation. It manifests the properties of neutron stars — change explicitly as different hyperon coupling constants are concerned.     

局域物态方程对中子星整体性质的影响

由于高密非对称核物质核核相互作用的复杂性,使得目前人们对高密非对称核物质的物态方程的认识还存在很大的不确定性。利用逐段修改物态方程的方法,探究了不同密度段物态方程对中子星整体性质的影响,尤其是对典型中子星（1.4 M_⊙）半径及最大质量的影响。研究进一步证实了在2倍饱和核密度附近的物态方程对典型质量中子星的半径有显著影响。还进一步分析了中子星的质量半径关系曲线特征及其斜率（dM/dR）对物态方程的依赖性,发现dM/dR主要由饱和核密度以上的中子星物质的物态方程决定。探索不同密度段物态方程对中子星整体性质的影响以及探索dM/dR对物态方程的依赖性,主要是为将来利用中子星的天文观测来反向约束致密物质的物态方程提供理论参考。Because of the complicacy of the interaction between the nucleon-nucleon for high density matters, up to now the equation of state (EOS) of the unsymmetrical high-density nuclear matter is still uncertain. In order to investigate the imprint on the global properties by some special part of the EOS, we designedly modify part of the EOS and explore the corresponding effect on the stellar properties, especially on the radius of the typical neutron star (1.4 M_⊙) and the maximum stellar mass of the neutron star sequence for a given EOS. It is further proved by our calculation that the EOS around 2 times of the saturation nuclear density has an obvious imprint on the stellar radius of a typical neutron star. In addition, we also investigate the dependence of the mass-radius curve and its slope (dM/dR) on the EOS. It is found that the slope (dM/dR) is mainly determined by the EOS above the saturation nuclear density. In fact, the investigations above will provide some useful theoretical reference. This is expected to conversely constrain the EOS of dense matter by using the future astronomic observation data of neutron star.     

Influence of Density-Dependent Coupling Constants on Equation of State of Infinite Symmetric Nuclear Matter

In the mean field approximation of nonlinear relativistic σ-ω-ρ model, we have studied the influence of density-dependent coupling constants between nucleons and mesons on the equation of state (EOS) of infinite symmetric nuclear matter in different conditions. We find that the EOS of nuclear matter will become stiffer as c, d in the self-interaction of σ meson increase when the coefficients except a_ω in Γ_ω, in which the opposite occurs, are fixed. On the other hand, greater values of a_σ, b_σ, c_σ, a_ω, d_ω and smaller values of d_σ, b_ω, c_ω will lead to stiffer EOS if c and d are fixed. Besides, greater values of Γ _σ,ω lead to stiffer EOS in high density region for the EOS with same incompressibility coefficient at saturation density.     

天体物理、引力波及重离子碰撞中的物质

通过相对论性磁流体力学的计算知道,由双中子星合并产生的引力波对中子星内部是否存在夸克物质以及QCD物质状态方程的硬度度非常敏感。这些天文学上创造的热力学极限在20%以内跟某些快度、碰撞参数等条件下的相对论重离子碰撞产生的温度和密度相当。本文结合相对论模拟双中子星系统及实验室中重离子碰撞的结果,从而确定高密物质的状态方程和相结构。讨论了中子星合并后残留物的引力波发射,这将有助于了解夸克强子过渡的性质。     

Isoscalar and isovector nuclear matter properties and neutron skin thickness

Isoscalar and isovector nuclear matter properties are investigated in the Skyrme Hartree-Fock (SHF) and the relativistic mean field (RMF) models. The Skyrme parameters are related analytically to the isoscalar and the isovector nuclear matter properties of the Hamiltonian density. Linear correlations are found among the isovector nuclear matter properties of the Hamiltonian density in both the SHF and the RMF models. We also discovered that the correlations between the isovector properties and the incompressibility K show a singularity at the critical incompressibility K_c=306 MeV. It is shown that the neutron skin thickness gives crucial information about not only for the neutron EOS but also about the isovector nuclear matter properties and about the parameterization of Skyrme interaction. Charge exchange spin-dipole (SD) excitations are proposed to determine the neutron skin thickness model independently.     

Quark deconfinement in neutron star cores

Whether or not the deconfined quark phase exists in neutron star cores is an open question. We use two realistic effective quark models, the three-flavor Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to describe the neutron star matter. We show that the modified quark-meson coupling model, which is fixed by reproducing the saturation properties of nuclear matter, can be consistent with the experimental constraints from nuclear collisions. After constructing possible hybrid equations of state (EOSes) with an unpaired or color superconducting quark phase with the assumption of the sharp hadron-quark phase transition, we discuss the observational constraints from neutron stars on the EOSes. It is found that the neutron star with pure quark matter core is unstable and the hadronic phase with hyperons is denied, while hybrid EOSes with a two-flavor color superconducting phase or unpaired quark matter phase are both allowed by the tight and most reliable constraints from two stars Ter 5 I and EXO 0748-676. And the hybrid EOS with an unpaired quark matter phase is allowed even compared with the tightest constraint from the most massive pulsar star PSR J0751+1807.     

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。     

Nuclear matter properties in the relativistic Λ-approximations

In the framework of relativistic nuclear field theory the nuclear matter parameters were calculated in the so-called Λ⁰⁰- and approximation of the Green function theory. For the nucleon-meson coupling constants we used parameter sets given by the Bonn and Groningen group. The results show no significant differences with those obtained from the relativistic Brueckner theory.     

N－N关联和有限核相对论平均场方法

密度有关的核子－介子相互作用耦合常数是在相对论平均场近似下用核物质的相对论Ｂｒｕｅｃｋｎｅｒ－Ｈａｒｔｒｅｅ－Ｆｏｃｋ近似计算的自能参数化得到的．这种密度有关的相互作用考虑了介质中Ｎ－Ｎ关联效应，用这种密度有关的相互作用来研究有限核的基态性质，如单粒子能级，平均结合能，电荷均方根半径，与实验值较好地符合，同时还与其它模型的结果进行了比较。     

An equation of state for nuclear and higher-density matter based on relativistic mean-field theory

A model stress tensor for high-density matter based on a linearized relativistic quantum field theory is examined. The two coupling constants are fit to nuclear matter. Other properties of nuclear and neutron matter and neutron stars are then implied.     

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.     

Neutron stars including the effects of chaotic magnetic fields and anomalous magnetic moments

The relativistic mean field(RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields.The chaotic magnetic field approximation is utilized.The effect of anomalous magnetic moments(AMMs) is also investigated.It is shown that the equation of state(EOS)of neutron star matter is stiffened by the presence of the magnetic field,which increases the maximum mass of a neutron star by around 6%.The AMMs only have a small influence on the EOS of neutron star matter,and increase the maximum mass of a neutron star by 0.02M_(sun).Neutral particles are spin polarized due to the presence of the AMMs.