对称性、对称性破缺和相变

本文将扼要介绍物理学中对称性的分类及其特征,说明对称性破缺与一物理系统从无序到有序的相变过程间的关系,并讨论了对称性破缺出现的前提     

对称性,对称性破缺和相变

本文将扼要介绍物理学中对称性的分类及其特征，说明对称性破缺与一物理系统从无序到有序的相变过程间的关系，并讨论了对称性破缺出现的前提。     

动力学自发破缺的模型在有限温度和密度下的状态方程和相结构

本文在Lurie模型的基础上,建立了一种近似计算状态方程的方法.得到了Lurie模型的状态方程所满足的参数方程.该模型的手征相变的相图表明:存在一个临界点c将一级相变和二级相变分开.仔细分析压强对净重子数密度的等温线,其结果表明:发生一级相变时,有过冷和过热的亚稳态,存在有自发破缺的破缺相和无自发破缺的正常相的两相共存.     

关于对称破缺的一些体会

考察了对称破缺的数学形式及物理本质,说明了对称破缺、各态历经假设及序参量空间的一些简单联系,并希望通过这种联系能够更深刻地理解相变、亚平衡等概念,增加热力学和统计力学的统一性。     

磁场中有限长铁钉稳定位形和相变

磁铁附近磁场中铁钉站立和倒下是一个常见的现象,本文通过计算无限长导线、平行无限长导线及圆环电流磁场中有限长度铁钉势函数,分析势函数稳定点的位置来判断铁钉的指向。当考虑铁钉固有磁矩后,铁钉移动过程中所处位置由一个亚稳定点变成了一个非稳定点,铁钉随后就倒向了稳定点。我们利用描述对称性破缺的朗道连续相变理论来分析相变之后稳定位形的具体规律。结果表明相变之后稳定位形与朗道连续相变理论预言的临界指数非常符合,铁钉的站立和倒下这样常见现象可以作为讲解相变理论经典力学例子。理论物理的抽象概念在经典物理世界找到对应,深刻体现了物理理论的美妙。     

具有动力学破缺的模型在有限温度和密度下的手征相变

作为一种定性的指导,本文用近似方法考察了具有动力学破缺的模型的手征对称性恢复相变.建立了模型的自洽方程;给出了费米子的凝聚和质量以及系统的能量密度和比热对温度和密度的依赖关系.结果表明在零化学势和有限温度情况,手征相变是二级相变,而在有限温度和密度及零温有限密度情况,手征相变是一级相变且从破缺相到正常相的转变温度或密度不同于从正常相到破缺相的转变温度或密度.     

对称性与对称的破缺性

对称与对称破缺是自然界中普遍存在着的一种矛盾关系。对称是变化中的同一 ,反映不同物质形态在运动中的共性 ,破缺是变化中的差异 ,反映不同物质形态在运动中各自的特性。自然界的物质 (包括整个自然界在内 )处于对称→对称破缺→深一级对称→对称性又破缺……这样不断深化之中     

手征破缺模型与饱和核物质的热力学性质

本文在平均场理论框架下用手征破缺模型研究了不同温度区域饱和核物质的热力学性质.改进并推广了Chowdhury等人的结果,通过费米积分的数值积分确认了Chowdhury等处理核物质低温高密度系统近似方法的适用范围为βμ_eff>2.4,给出了(液)-(气)相变临界温度T_c≌23MeV,并得到核子-反核子等离子体相变区域为T=150～200MeV.     

玻色-爱因斯坦凝聚体中的超流现象

在玻色-爱因斯坦凝聚(BEC)的超流现象的研究中,人们通常采用平均场近似下求解Gross-Pitaevskii方程的方法,我们采用更严格的准确对角化的方法对弱排斥相互作用下两维旋转N-Boson体系的凝聚状态进行了研究.研究表明,弱相互作用下的基态并不是人们通常认为的单一凝聚态,而是一个碎裂凝聚态.通过碎裂态能谱与平均场方法给出的能谱之间的比较以及条件几率分布函数的计算,我们指出这种碎裂凝聚态有着内在的不稳定性,很容易破缺到一个单一凝聚状态;计算给出的条件几率分布可以用来揭示破缺后的状态,其分布图案与平均场近似下所得到的涡旋图形相类似.我们进一步注意到过去研究工作主要集中在弱相互作用极限下和强相互作用Thomas-Fermi近似极限下这两种极端情况.为考察两种极限间的中间过渡区域,我们研究了中等相互作用强度下体系的基态性质.     

顶色辅助的人工色模型下顶夸克极化效应的研究

在顶色辅助的人工色(TC2)理论下, 在强子对撞机上研究了顶夸克-反顶夸克对的产生过程中顶夸克的极化效应, 在计算过程中, 运用了MRS set A'部分子分布函数和螺旋度投影算符的方法. 研究结果表明: 在Tevatron上顶夸克的极化效应太小不可探测; 参数选取得当, 该效应在LHC上可以探测到, 其值可达16%. 因此, 顶夸克的极化效应提供了一种切实可行的检验顶色辅助的人工色模型的方法.     

Critical Analyses of Order Parameter and Phase Transitions at High Density in Gross-Neveu Model

By critical analyses of the order parameter of symmetry breaking, we have researched the phase transitionsat high density in D = 2 and D = 3 Gross-Neveu (GN) model and shown that the gap equation obeyed by the dynamicalfermion mass has the same effectivenesss as the effective potentials for such analyses of all the second order and somespecial first order phase transitions. In the meantime we also further ironed out a theoretical divergence and proventhat in D = 3 GN model a first order phase transition does occur in the case of zero temperature and finite chemicalpotential.     

Critical Analyses of Order Parameter and Phase Transitions at High Density in Gross－Neveu Model

By critical analyses of the order parameter of symmetry breaking, we have researched the phase transitions at high density in D = 2 and D = 3 Gross-Neveu (GN) model and shown that the gap equation obeyed by the dynamical fermion mass has the same effectivenesss as the effective potentials for such analyses of all the second order and some specJal first order phase transitions. In the meantime we also further ironed out a theoretical divergence and proven that in D = 3 GN model a first order phase transition does occur in the case of zero temperature and finite chemical potential.     

Color Superconductivity in Cold Dense Quark Matter

We investigate the phase structure of color superconducting quark matter at intermediate densities for two- and three-flavor systems. We thereby focus our attention on the influence of charge neutrality conditions as well as -equilibrium of the different phases. These constraints are relevant in the context of quark matter at the interior of compact stars. We analyze the implications of color superconductivity on compact star configurations using different hadronic and quark equations of state.Presented at the 15th Indian-Summer School of Physics: Understanding Dense Matter, Prague, Czech Republic, 27 August–1 September, 2003.     

拉曼峰强作为分子晶体相变的有序度

本文介绍以拉曼峰强为分子晶体相变有序度的概念，并以ＫＨ＿（１－ｘ）Ｄ＿（ｘ）Ｆ＿２和Ｋ＿（１－ｘ）Ｎａ＿（ｘ）Ｆ＿２为例说明晶格振动模在相变过程中的临界性质可以因此得到。晶格振动模的临界性质反映着掺杂体系的丰富信息。     

Calculation of Quark Condensate in Nuclear Matter with the Chiral Symmetry Spontaneous Breaking Lagrangian

Using the chiral symmetry spontaneous breaking Lagrangian with mean-field approximation, we investigate the in-medium quark condensate 〈qq〉. It is found that the condensate decreases as the nuclear matter density ρ increases. Meanwhile, the desent deviates from the linear decrease and becomes remarkably slow as the density of the nuclear matter further increases. It shows that the chiral symmetry spontaneous breaking is only partially restored in densed nuclear matter.     

二维３态Potts量子系统的保真度与序参量

二维无限正方格子上的量子3态Potts模型是发生一级相变还是二级相变?通过运用无限纠缠投影对态算法(iPEPS),在进行数值模拟时任意选取初态,能得到二维无限正方格子上的3态Potts模型的三个不同的简并基态波函数,这些简并的情况是由自发对称性破缺引起的.首先,揭示了在二维系统中自发对称性破缺引起的相变可以运用单点基态保真度的分叉来研究,也反映了在二维系统中约化保真度同样有一个分叉行为;再者,还开创性提出了二维系统的普适序参量以及多分量的复数局域序参量的行为来尝试研究二维3态Potts模型,共同确定系统发生的量子相变的临界点及其类型.即基于iPEPS算法,从单点基态保真度、约化保真度、普适序参量以及局域序参量的角度,来研究3态Potts模型的量子相变,其为一级相变.     

Determination of the Order Parameter in Binary Fluid Mixtures

We propose a microscopic approach to the study of phase transitions in fluid mixtures. It is based on the collective variables method with a reference system. The problem of definition of the order parameter in a two-component fluid system is considered in detail. This system is described with two sets of collective variables: _k and _k. It is shown that the CV connected with the order parameter is _k=0 in the case of a gas–liquid critical point as well as in the case of a mixing–demixing phase transition. The relations between the microscopic parameters, temperature, density and concentration which determine the particular form of ₀ for each of these phenomena are obtained. Based on these results we will be able to construct an effective Ginsburg–Landau–Wilson Hamiltonian.     

Quark Condensate in the Strange Matter

In a nonlinear chiral SU(3) framework, we investigate the quark condensate in the strange matter including N, Σ, Ξ, and Λ, making use of chiral symmetry spontaneous breaking Lagrangian and mean-field approximation. The results show that the chiral symmetry is restored partially when the strange matter density increases and that 〈π→2〉 plays a very important role in the strange matter which may approach the constituents of the neutron stars. In addition, we can find that the strange matter density where the π-condensate emerges leads to the ratio of the nucleon number to baryon number.     

核物质热力学性质的同位旋和动量相关性

利用3个具有不同的同位旋和动量相关性的热力学模型研究了非对称核物质的热力学性质, 它们是重离子碰撞中同位旋弥散数据约束下的、 同位旋和动量相关的MDI模型, 完全动量无关的MID模型, 以及同位旋标量动量相关的extended MDYI(eMDYI)模型。 主要研究了同位旋非对称热核物质的对称能和系统力、 化学不稳定性以及液气相变的温度效应。 MDI模型对称能的温度效应来源于动能和势能两部分贡献, 而MID和eMDYI模型只有势能部分对对称能的温度效应有贡献。 研究结果还表明, 力学不稳定性区域、 化学不稳定性区域和液气共存区都依赖于模型的同位旋和动量相关性, 以及对称能的密度依赖关系。In this article, three models with different isospin and momentum dependence are used to study the thermodynamical properties of asymmetric nuclear matter. They are isospin and momentum dependent MDI interaction constrained by the isospin diffusion data of heavy ion collision, the momentum independent MID interaction and the isoscalar momentum dependent eMDYI interaction. Temperature effects of symmetry energy, mechanical and chemical instability and liquid gas phase transition are analyzed. It is found that for MDI model the temperature effects of the symmetry energy attribute from both the kinetic and potential energy, while only potential part contributes to the decreasing of the symmetry energy for MID and eMDYI models. We also find that the mechanical instability, chemical instability and liquid gas phase transition are all sensitive to the isospin and momentum dependence and the density dependence of the symmetry energy.     

热核物质液气相变的临界温度和三体核力效应

通过引入微观三体核力, 扩展了有限温度Brueckner-Hartree-Fock方法. 利用这一扩展的理论模型, 研究了热核物质的状态方程和液气相变现象并计算了临界温度, 讨论了三体核力对液气相变临界点性质的影响并与Dirac-Brueckner-Hartree-Fock方法的理论预言进行了比较. 结果表明：三体核力对热核物质状态方程提供一个随密度和温度增大而增强的排斥贡献, 而且三体核力的排斥效应导致热核物质液气相变的临界温度明显降低.