Influence of Different Y-Y Interactions on the Stability of Strange Hadronic Matter

An effective model is used to study the equation of state (EOS) of strange hadronic matter with nucleons, ∧-hyperons and Ξ-hyperons. In the calculation, a newest weak hyperon-hyperon (Y-Y) interaction deduced from the recent observation [Phys. Rev. Lett. 87(2001)212502-1] of a∧∧^6 He double hypernucleus is adopted. The calculated results are compared to those calculated with the strong Y-Y interaction used in previous studies.     

Hyperon--hyperon interaction in relativistic mean field model

By using the new experimental data of \Lambda\Lambda potential, this paper has performed a full calculation for strange hadronic matter with different strangeness contents as well as its consequences on the global properties of neutron star matter in relativistic mean field model. It finds that the new weak hyperon--hyperon interaction makes the equations of state much stiffer than the result of the previous strong hyperon--hyperon interaction, and even stiffer than the result without consideration of hyperon--hyperon interaction. This new hyperon--hyperon interaction results in a maximum mass of 1.75M_{\odot} (where M_{\odot} stands for the mass of the Sun), about 0.2--0.5M_{\odot} larger than the previous prediction with the presence of hyperons. After examining carefully the onset densities of kaon condensation it finds that this new weak version of hyperon--hyperon interaction favours the occurrence of kaons in comparison with the strong one.     

奇异强子与核子的相互作用

包含s夸克的强子称为奇异强子,它与核子相互作用的研究近年来有了长足发展 .在指出这种研究的重要意义后,从实验和理论两方面介绍奇异强子 (主要是K介子和超子 )与核子相互作用的研究现状及方法等 ,包括运动学和动力学机制、介子交换模型和夸克模型解释诸方面的问题. We try to highlight some of the key issues regarding the interactions between strange hadron and nucleon, which relate to the kinematics and dynamics mechanism, meson exchange model and quark model. Starting from a brief introduction on the main research goals, we focus on the status of experimental and theoretical investigations of kaon nucleon and hyperon nucleon interactions, which may be considered to be a necessary basis for the studies of nuclear physics with strangeness.     

相对论平均场理论对∧,Ξ和∑超核的研究(英文)

基于相对论平均场理论,系统地研究了单∧,Ξ和∑超核,超子-核子相互作用通过拟合实验数据以及参照之前理论工作来确定。以16O为核芯,通过加入不同类型超子（∧,Ξ0,-和∑+,0,-）,比较了超子的平均势场和单粒子能级,并研究了对核芯的杂质效应。整体上看,∧和Ξ0超子在大块性质上类似;Ξ0超子平均势场最浅;库仑相互作用对于带电超子Ξ-,∑+和∑-非常重要。作为杂质,原子核中加入超子会使整个体系更束缚。然而,不同超子对原子核的半径有不同效应。此外,讨论了ωYY张量耦合,发现其对超子的能级劈裂有显著影响,甚至导致Ξ超子中出现能级反转现象。Single ∧, Ξ, and ∑ hypernuclei are systematically studied within the framework of relativistic mean-field (RMF) model with YN interactions being constrained according to the experimental data and previous theoretical efforts. By adding a hyperon to 16O, the mean-field potentials and single-particle levels for hyperons (∧, Ξ0,-, and ∑+,0,-) are compared and the impurity effects on the nuclear core are examined. In general, the ∧ and ∑0 hyperons show similar behaviors in bulk properties since both of them are electroneutral and with similar coupling constants; Ξ0 hyperon owns the shallowest mean-field potential well; and Coulomb interactions play vital roles in the charged Ξ-, ∑-, and ∑+ hyperons. As an impurity, the intruded single-hyperon makes the nuclear system more bound in most cases due to the attractive NY interaction. However, very different effects on the nucleon radii are observed for different hyperons. Besides, the effects of the ωYY tensor couplings on the spin-orbit splitting are discussed, and remarkable influences are found which even change the level ordering of Ξ hyperon.     

Tetraneutron in the Chiral Quark Model

The tetraneutron state is studied in the framework of the chiral quark model with tetrahedron configuration. The universal attraction property of σ-meson exchange leads to a strong attraction in the effective potential of the system. It is possible to form a bound state. For comparison, the naive quark model is also employed to carry out the calculation. A weak attraction, which is too weak to bind the system, is obtained.     

Particle-hole bound states of dipolar molecules in an optical lattice

We investigate the particle-hole pair excitations of dipolar molecules in an optical lattice, which can be described with an extended Bose-Hubbard model. For strong enough dipole-dipole interaction, the particle-hole pair excitations can form bound states in one and two dimensions. With decreasing dipole-dipole interaction, the energies of the bound states increase and merge into the particle-hole continuous spectrum gradually. The existence regions, the energy spectra and the wave functions of the bound states are carefully studied and the symmetries of the bound states are analyzed with group theory. For a given dipole-dipole interaction, the number of bound states varies in momentum space and a number distribution of the bound states is illustrated. We also discuss how to observe these bound states in future experiments.     

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.     

Contributions of qqqq components to nucleon spin structure

The spin structure of nucleons is presented in the framework of an extended quark model which in addition to the conventional qqq structure also takes into account qqqq admixtures in the nucleon wave functions, where the qqqq components are in colored quark cluster configurations. The axial vector weak coupling constant and spin distributions for polarized nucleons as well as spin content are obtained for the lowest positive parity qqqq configurations in flavor-spin dependent interaction. In particular, the contributions of the down and strange quarks to the proton spin and the sum rule for polarized neutron are negative, in agreement with recent experiments.     

超子耦合参数对热前中子星物质的影响

在相对论平均场理论框架内,利用Λ超子的结合能和中子星质量的观测数据得到超子标量介子耦合参数χσ的范围是0.33—0.77。在这个范围内, 研究了χσ取不同值时, 包含核子, Λ和Ξ超子的热前中子星（固定单个重子熵s=1）的性质。结果表明, 如果超子耦合参数变大, 前中子星核心温度变高, 中微子丰度变低, 前中子星的亚稳态质量范围变小。如果χσ超过了0.75, 前中子星不可能演变成黑洞。联系SN1987A讨论了这一结果的意义。In the framework of the relativistic mean field theory(RMFT), protoneutron stars with hyperons are studied. To be compatible with neutron star masses, the hyperon scalar coupling χσ should lie in the range of 0.33—0.77. As the hyperon scalar coupling increases, in protoneutron star matter, the core temperature increases whereas the abundance of neutrinos decreases. The metastable mass range of protoneutron stars narrows as the temperature increases. It is found that a protoneutron star cannot subside into a low mass black hole when χσ>0.75. Furthermore, the case of SN1987A is discussed.     

奇异强子物质的有效模型描述

把 FST模型推广到包含奇异性的情形,并在平均场近似下用它来研究含有核子、Λ超子和Ξ超子的奇异强子物质的性质.讨论了有效重子质量对介质密度和奇异数含量的依赖性以及奇异强子物质的饱和性和稳定性. The strange hadronic matter with nucleon, Λ hyperon and Ξ hyperonis was studied by using an effective model in a mean field approximation. The density dependence of the effective baryon masses as well as the saturation properties and stabilities of the strange hadronic matter were discussed. The result indicates a quite large strangeness fraction range where the multi hyperon nuclear matter is stable against particle emission. In the large strangeness fraction region the Ξ component dominates...     

A Monte Carlo Study of Lambda Hyperon Polarization at BM@N

Heavy strange objects (hyperons) can provide essential signatures of the excited and compressed baryonic matter. At NICA, it is planned to study hyperons both in the collider mode (MPD detector) and the fixed-target one (BM@N setup). Measurements of strange hyperon polarization can give additional information on the strong interaction mechanisms. In heavy-ion collisions, such measurements are even more valuable since the polarization is expected to be sensitive to characteristics of the QCD medium (vorticity, hydrodynamic helicity) and to QCD anomalous transport. In this analysis, the possibility to measure at BM@N the polarization of the lightest strange hyperon Λ is studied in Monte Carlo event samples of Au + Au collisions produced with the DCM-QGSM generator. It is shown that the detector will allow to measure polarization with a precision required to check the model predictions.     

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.     

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.     

Strange hadronic matter in a modified quark-meson coupling model

Strange hadronic matter with nucleons, Λ-hyperons and Ξ-hyperons is studied by using a modified quark-meson coupling (MQMC) model in a mean-field approximation. The density dependence of the effective baryon masses as well as the saturation properties and stabilities of the strange hadronic matter are discussed.     

Self-consistently thermodynamic treatment for strange quark matter in the effective mass bag model

In the framework of the effective mass bag model (EMBM) we have performed the thermodynamical treatment for strange quark matter (SQM) self-consistently, which overcomes the inconsistencies in the thermodynamical properties of the system. Because of the existence of the pressure extra term, the SQM equation of state (EOS) becomes stiffer comparing with the one for the original EMBM. It is interesting to find that in our treatment the SQM EOS is almost independent of the strong coupling constant g . In this case the SQM EOS seems to get back to the EOS for the original MIT bag model. However, this treatment still has influence on the EOS for hybrid star matter and the corresponding mass-radius relations. With the increase of the strong coupling constant g , the EOS for hybrid star matter gets obviously stiff. From our treatment we notice that the pressure extra term can make a hybrid star more compact than the one described in the original EMBM and this model is more suitable to describe the hybrid stars with small radii.     

Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies

We investigate the relativistic equation of state of hadronic matter and quark-gluon plasma at finite temperature and baryon density in the framework of the non-extensive statistical mechanics, characterized by power-law quantum distributions. We impose the Gibbs conditions on the global conservation of baryon number, electric charge and strangeness number. For the hadronic phase, we study an extended relativistic mean-field theoretical model with the inclusion of strange particles (hyperons and mesons). For the quark sector, we employ an extended MIT-Bag model. In this context we focus on the relevance of non-extensive effects in the presence of strange matter.     

超子及K介子衰变的分枝比和平均寿命间的比例

本文应用了费曼和盖尔曼所提出的普适费米弱相互作用和同位旋守恒的强相互作用计算了各种超子、K介子衰变的分枝比和平均寿命的比例。在计算时应用了微扰论,并在大动量处将相互作用截断。在应用了查尔斯·瓦纳所给出的相互作用常数和对其余两个常数作了一定的选择之后,得到的分枝比和平均寿命之比大部分和实验结果符合,最坏相差一个因子二。如果选择本文所采用的相互作用常数,可以改进前一篇源文中K⁺介子分枝比计算结果和实验的符合程度。本文计算表明V-A普适弱相互作用确实适用于K分子和超子衰变现象,表明在解释这些现象时,必须考虑到“很强”和“较强”两类强相互作用所分别产生的影响。此外,本文还表明Λ和∑应具有相同的相对宇称,K分子和核子、超子之间的四种强相互作用中必须至少有一对是膺标量耦合。