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...     

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.     

密度相关的相对论平均场理论对核物质和中子星的描述

基于密度相关有效相互作用的相对论平均场理论,研究了核物质和中子星的性质.对核物质的饱和性质,密度相关的相互作用DD-ME1和TW-99给出了与NL1,NL3,NLSH,TM1基本一致的结果;NL2和TM2主要用于计算轻核,与它们的结果差别较大.对于中子星,在低密度区域,各种相互作用给出的介子势场差别不大;在高密度区域,相应的介子势场的差别随密度增加而增大.密度相关的相互作用DD-ME1和TW-99,与NL1,NL3和NLSH的结果相比,其物态方程明显偏软.相应的中子星的最大质量也不同,不同有效相互作用给出的最大质量为2.0—3.0M⊙,从大到小的顺序依次是NLSH?,NL3,NL1,DD-ME1,TW-99,TM1和GL-97,对应的半径为10—14km.     

中子星物质中的K－,K0凝聚

采用相对论平均场理论研究K凝聚对中子星物质的影响. 研究发现即使在含重子八重态和Δ共振态(n,p,Λ,Σ⁺,Σ⁰,Σ^－,Ξ⁰,Ξ^－,Δ⁰,Δ^－)的中子星物质中,K^－, K⁰凝聚也可以发生, 并详细研究了超子与K凝聚相互影响的行为. K⁰凝聚压低K^－凝聚, 促进Δ共振态的出现, 在中子星的核心区域, 最终形成多种重子共存的、各重子数密度趋于均衡、且K⁰凝聚占最大比重的中子星物质. K凝聚使物态方程变软, 进而减小中子星的最大质量, 使之更接近于中子星正则质量.     

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.     

新生中子星的性质与三体核力效应

在Brueckner-Hartree-Fock理论框架内, 研究了新生中子星的状态方程和性质, 计算了新生中子星的最大质量和新生中子星中质子占总核子数的丰度, 特别是讨论了三体核力和中微子束缚效应的影响以及三体核力和中微子束缚效应的相互影响. 结果表明, 无论是否考虑三体核力, 中微子束缚对新生中子星的状态方程和质子丰度均有明显影响. 中微子束缚导致新生中子星物质中的质子丰度显著增大. 三体核力的贡献是使新生中子星的状态方程变硬并导致新生中子星中质子丰度明显增大. 束缚在中子星物质中的中微子显著减弱了三体核力对于中子星物质中质子丰度的影响.     

中子星内壳层的物态方程和质子丰度

求解了恒定均匀的强磁场中核子的能谱和波函数，在手征表象中给出含核子反常磁矩(AMM)项的Dirac方程的解；并且计算了中子星内壳层物质的物态方程(EOS)和粒子丰度，发现在强磁场中磁能将使中子星内壳层的压强增加但物质仍然是丰中子，AMM项对质子的极化度有明显效应.     

利用含δ介子的相对论平均场理论研究中子星潮汐形变性质

开展中子星宏观性质的研究,对于揭示中子星内部组成和结构具有重要意义.本文基于相对论平均场理论模型,研究了δ介子对传统中子星和超子星物态方程、最大质量、勒夫数和潮汐形变能力的影响.结果表明,对于中小质量传统中子星(或超子星), δ介子使其潮汐形变能力变强;随着传统中子星(或超子星)质量的增加, δ介子对其潮汐形变能力影响逐渐减弱;尤其对于大质量超子星,含有δ介子的超子星潮汐形变能力相比不含δ介子的超子星变弱.此外,在相同质量下超子的存在会降低星体的潮汐形变能力,在本文所选的参数下,含有δ介子的星体中,仅同时含L,Σ和Ξ超子的超子星潮汐形变能力能同时满足GW170817和GW190814天文观测约束.随着与中子星相关的引力波数据逐渐增加,将为人们判断超子星内超子种类提供一个可能的途径.     

f0(975)和φ(1020)介子对中子星物质的影响

利用相对论平均场理论,考虑了σ*,φ介子及重子八重态{N,P,A,∑-,∑0,∑ ,(I)-,(I)0},研究了中子星的性质.发现当考虑了σ*,φ介子的贡献时,超子出现的临界重子数密度降低了,超子数目增加了,超子星的转变密度ρ0H降低了,物态方程变软,最大质量变小而相应的中子星半径增大,中子星的中心重子数密度、中心能量密度和中心压强均降低.     

f0（975）和Ф（1020）介子对中子星物质的影响

利用相对论平均场理论，考虑了σ＊，Ф介子及重子八重态{N，P，A，∑^-，∑0,∑＋，Ξ^-，Ξ^0}，研究了中子星的性质．发现当考虑了σ＊，Ф介子的贡献时，超子出现的临界重子数密度降低了，超子数目增加了，超子星的转变密度poH降低了，物态方程变软，最大质量变小而相应的中子星半径增大，中子星的中心重子数密度、中心能量密度和中心压强均降低．     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

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.     

Spin polarised nuclear matter and its application to neutron stars

An equation of state (EOS) of nuclear matter with explicit inclusion of a spin-isospin dependent force is constructed from a finite range, momentum and density dependent effective interaction. This EOS is found to be in good agreement with those obtained from more sophisticated models for unpolarised nuclear matter. Introducing spin degrees of freedom, it is found that it is possible for neutron matter to undergo a ferromagnetic transition at densities realisable in the core of neutron stars. The maximum mass and the surface magnetic field of the neutron star can be fairly explained in this model. Since finding quark matter rather than hadronic matter at the core of neutron stars is a possibility, the proposed EOS is also applied to the study of hybrid stars. It is found using the bag model picture that one can in principle describe both the mass as well as the surface magnetic field of hybrid stars satisfactorily.     

Neutron star in the presence of strong magnetic field

Compact stars such as neutron stars (NS) can have either hadronic or exotic states like strange quark or colour superconducting matter. Stars can also have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and the quark phases. Observational results suggest huge surface magnetic field in certain NS. Therefore, we study here the effect of strong magnetic field on the respective equation of states (EOS) of matter under extreme conditions. We further study the hadron–quark phase transition in the interiors of NS giving rise to HS in the presence of strong magnetic field. The hadronic matter EOS is described based on RMF theory and we include the effects of strong magnetic fields leading to Landau quantization of the charged particles. For quark phase, we use the simple Massachusetts Institute of Technology (MIT) bag model, assuming density-dependent bag pressure and magnetic field. The magnetic field strength increases from the surface to the centre of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. We finally study, the mass–radius relationship for such types of mixed HS, calculating their maximum mass, and compare them with the recent observations of pulsar PSR J1614-2230, which is about 2 solarmass.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

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.     

Bose-Einstein condensation of anti-kaons and neutron star twins

We investigate the role of Bose-Einstein condensation (BEC) of anti-kaons on the equation of state (EoS) and other properties of compact stars. In the framework of relativistic mean field model we determine the EoS for β-stable hyperon matter and compare it to the situation when anti-kaons condense in the system. We observe that anti-kaon condensates soften the EoS, thereby lowering the maximum mass of the stars. We also demonstrate that the presence of antikaon condensates in the high density core of compact stars may lead to a new mass sequence beyond white dwarf and neutron stars. The limiting mass of the new sequence stars is nearly equal to that of neutron star branch though they have distinctly different radii and compositions. They are called neutron star twins.     

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.     

前中子星内的K-凝聚和超子的生成

用相对论平均场下的手征强子模型研究了前中子星内K^-凝聚和超子的生成。结果显示，前中子星内的中微子束缚使得出现K^-凝聚的临界密度推迟到更高的重子密度，而K^-0凝聚无法出现。同时中微子束缚使得前中子星的状态方程变硬，从而前中子星的最大质量变大。如果考虑超子，前中子星内无法出现K^-凝聚，同时系统的状态方程变软（与不含超子的情况相比），从而对应前中子星的最大质量变小。A chiral hadronic model is extended to investigate antikaon condensation and hyperons production of protoneutron stars. Our results show that neutrino trapping makes the critical density of K^- condensation delay to higher density and K^-0 condensation not occur. Meanwhile, the equation of state （EOS） of （proto）neutron star matter considering neutrino trapping is stiffer than the case without neutrino trapping. Therefore the maximum masses of rotoneutron stars with neutrino trapping are larger than those without neutrino trapping. If hyperons are considered, antikaon condensation does not appear 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.