强相互作用系统的对称性及其破缺

本文简要介绍对称性及其破缺的概念和基本的数学上所说的幺正对称性等的微观粒子实现，从而为利用抽象的数学描述物理问题奠定基础。本文还简要介绍早期宇宙强相互作用物质演化过程的对称性及其破缺，尤其是可见物质质量的产生(比如DCSB)以及强相互作用等基本相互作用的规范对称性和破缺，为有意向探讨早期宇宙强相互作用物质演化的青年学者和研究生提供必要的知识储备，并打开一扇窗口。同时，还简要讨论原子核的对称性及其破缺，尤其是作为强相互作用多体系统的束缚态研究中的基本理论方法、(多粒子)壳模型及相互作用玻色子近似模型(IBM)、集体运动的描述及集体运动模式演化(形状相变)的研究方法及进展简况，提供一些在基本理论方法与前沿研究课题之间建立桥梁的实例。     

对称性自发破缺与规范理论

一、引 言 基本粒子间的相互作用具有各种对称性,其中有些是严格对称的,有些只是近似地满足对称性要求,后者称为被破坏的对称性.被破坏的对称性又可分两类:一是象微扰项那样的某种外部原因使对称性遭到破坏的;二是由于某种内部原因使对称性自发地被破坏的.这后者我们称为对称性的自发破缺. 用对称性自发破缺理论,成功地解释了超导性和铁磁性等物理现象.因此,把它推广到基本粒子理论里的工作,曾引起了广泛兴趣. 若存在有对称性自发破缺,那末同时必然会出现Goldstone玻色子,但在目然界里至今还没有发现过这种粒子.Higgs机制解决了如何避免出…     

夸克与对称性自发破缺

用普通物理和原子物理的语言论述了对称性破缺机制和理论模型,介绍了2008年度诺贝尔物理学获奖者小林诚(Makoto Kobayashi)、益川敏英(Toshihide Maskawa)关于弱相互作用的理论模型(KM模型)和对称性破缺的起源,它是对电弱统一理论的完美补充;详细分析了在微观粒子世界系列实验中对称性自发破缺和夸克的发现.     

世纪交替期物理学的两大困惑

 物质结构的新层次夸克禁闭相互作用的规范理论 电磁场相互作用的规范理论 扬米尔斯场对称性自发破缺 希格斯机制困惑与方向     

高压流体相平衡的分子热力学模型

本文应用物质分子聚集与解集理论阐述了高压流体相平衡机理并提出了分子聚集型状态方程.应用此方程能精确地描述流体高压下的PVT关系,且用于预测相平衡数据也获得了满意结果.     

生命起源中的对称性破缺

生命起源中的对称性破缺─—分子的手性是生物学中长期困惑不解的难题。自然界中组成蛋白质的氨基酸几乎都是Ｌ型。最近萨拉姆提出，由于Ｚ°相互作用结合玻色凝聚态理论，在某临界低温有可能引起氨基酸由Ｄ向Ｌ型的二级相变，并通过非线性化学动力学将对称破缺放大。     

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     

分子间相互作用对核酸碱基中17O屏蔽张量与四极耦合常数影响的理论计算研究

通过高精度量子化学理论计算的方法研究了分子间弱的非键相互作用对胸腺嘧啶、尿嘧啶、胞嘧啶和鸟嘌呤四种核酸碱基中~(17)O核的屏蔽张量(σO)和四极耦合常数(QCC)的影响.计算结果表明分子间强的氢键作用以及弱的范德华(vd W)相互作用都对~(17)O核的化学位移(δO)具有较大的影响.随着分子间氢键作用的逐渐增强,δO逐渐减小,当采用包含所有弱相互作用的周期性模型进行计算时,理论结果与实验值吻合.进一步的电荷分析显示,~(17)O核化学位移的减小主要是由于分子间氢键作用强度增加导致~(17)O原子的负电荷密度逐渐增加.此外,计算结果表明碱基中分子间氢键网络和弱的范德华作用对碱基~(17)O QCC也具有显著的影响.周期性模型下,碱基上氧原子的局域结构环境得到平衡,~(17)O QCC达到最小值,与实验结果最为接近.以核酸碱基为例,说明了分子间的氢键网络以及分子间弱的相互作用对于准确计算生物样品的核磁共振(NMR)参数非常重要,以小的团簇模型来计算生物体系的核磁参数将会产生较大的偏差.     

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。     

一类三次方对称离散混沌系统的分岔控制

通过分析对称性破缺分岔机制, 采用了一个直接的、有效的线性控制器, 精确控制了一类三次方对称离散混沌系统发生对称性破缺分岔和倍周期分岔时分岔点的位置. 进而分析了系统对初始值的敏感性和对称性, 选择合适的吸引域, 将对称性破缺分岔进行进一步控制, 从而使得对称性破缺分岔所缺解枝得以恢复. 数值结果表明了该控制器的有效性. 关键词： 离散混沌系统 对称性破缺 倍周期 分岔控制     

Phase behavior and fluid-solid surface tension of argon in slit pores and carbon nanotubes

Phase behaviors of argon in several types of cylindrical and slit pores are examined by grand-canonical Monte Carlo simulations. Condensation processes in single- and multi-walled carbon nanotubes along with those in hard-wall tubes are compared. Effects of the pore size on pressure-tensor components, the fluid-wall surface tension, and the adsorption are also compared for the different fluid-pore interactions. The chemical potential at which the fluid begins to condense in the single-walled nanotube is greater than that in the multi-walled nanotube by an amount nearly equal to the difference in the potential-well depth of the fluid-pore interaction, and the adsorption isotherms overlap each other almost completely for narrow pores and partially for wider pores. Similar analyses are performed for slit pores of two different hydrocarbon models.     

Capillary smectization and layering in a confined liquid crystal

Using density-functional theory, we have analyzed the phase behavior of a model liquid crystal confined between two parallel, planar surfaces (i.e., the so-called slit pore). As a result of confinement, a rich phase behavior arises. The complete liquid-crystal phase diagram of the confined fluid is mapped out as a function of wall separation and chemical potential. Strong commensuration effects in the film with respect to wall separation lead to enhanced smectic ordering, which gives capillary smectization (i.e., formation of a smectic phase in the pore), or frustrated smectic ordering, which suppresses capillary smectization. These effects also produce layering transitions. Our nonlocal density-functional-based analysis provides a unified picture of all the above phenomena.     

Permanent confinement in the compact QED3 with fermionic matter

We argue that the compact three dimensional electrodynamics with massless relativistic fermions is always in the confined phase, in spite of the bare interaction between the magnetic monopoles being rendered logarithmic by fermions. The effect is caused by screening by other dipoles, which transforms the logarithmic back into the Coulomb interaction at large distances. Possible implications for the chiral symmetry breaking for fermions are discussed, and the global phase diagram of the theory is proposed.     

Entanglement, quantum phase transition and fixed-point bifurcation in the N-atom Jaynes-Cummings model with an additional symmetry breaking term

In the present work we analyze the quantum phase transition (QPT) in the N-atom Jaynes-Cummings model (NJCM) with an additional symmetry breaking interaction term in the Hamiltonian. We show that depending on the type of symmetry breaking term added the transition order can change or not and also the fixed point associated to the classical analogue of the Hamiltonian can bifurcate or not. We present two examples of symmetry broken Hamiltonians and discuss based on them, the interconnection between the transition order, appearance of bifurcation and the behavior of the entanglement.     

Swimmers in thin films: from swarming to hydrodynamic instabilities

We investigate theoretically the collective dynamics of a suspension of low Reynolds number swimmers that are confined to two dimensions by a thin fluid film. Our model swimmer is characterized by internal degrees of freedom which locally exert active stresses on the fluid. We find that hydrodynamic interactions mediated by the film can give rise to spontaneous continuous symmetry breaking (swarming), to states with either polar or nematic homogeneous order. For dipolar swimmers, the stroke averaged dynamics are enough to determine the leading contributions to the collective behavior. In contrast, for quadrupolar swimmers, details of the internal dynamics are important in determining the bulk behavior. In the broken symmetry phases, fluctuations of hydrodynamic variables destabilize order. Interestingly, this instability is not generic and depends on the length scale.     

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。     

Symmetry behavior in gauge theories

A theory of phase transition with symmetry restoration in gauge theories at high temperature is investigated. The phase transition may be of the first or of the second order depending on relations between coupling constants. It is noted that the possible existense of a limiting temperature cannot prevent the high-temperature symmetry restoration. In the theories without neutral currents, symmetry also can be affected by a magnetic field. However in most of the models with neutral currents symmetry restoration takes place not due to a magnetic field but due to massive vector fields, created simultaneously by the magnetic field sources. It is pointed out that in most of the theories with neutral currents an increase of external currents lead to symmetry restoration, while an increase of density results in a further increase of symmetry breaking. In some cases critical values of temperature and external fields and currents appear to be extremely small. At certain relations between coupling constants radiative corrections lead to the absence of symmetry breaking in gauge theories even at zero temperature and in the absence of any other external factors. Strong constraints on masses and coupling constants for the symmetry in the Higgs model to be broken are obtained. It is shown that energy of substance is nonconserved due to energy “pumping” from the non-observable Bose-condensate in the processes under consideration.     

Molecular simulation study of triangle-well fluids confined in slit pores

Grand canonical Monte Carlo simulations are used to study the behaviour of triangle-well (TW) fluids with variable well widths confined inside slit pores. The effect of individual factors influencing the properties of confined fluids such as fluid–fluid interactions, pore size and pore wall–fluid interactions are obtained using simulations as it is difficult to experimentally determine the same. An interesting observation of this study is that inside the narrow pore of slit height h* = 5 at the high-pressure condition of P* = 0.8, for the TW fluid with long-range attraction or for the fluid at a low temperature for even a short-range attraction, the density profiles show layering such that there is a sticking tendency of the particles at centre, while there is a depletion of particles near the wall (as the layers at the centre have higher density peak heights than near the walls).     

Spontaneously broken quark helicity symmetry

We discuss the origin of chiral-symmetry breaking in the light-cone representation of QCD. In particular, we show how quark helicity symmetry is spontaneously broken in SU (N) gauge theory with massless quarks if that theory has a condensate of fermion light-cone zero modes. The symmetry breaking appears as induced interactions in an effective light-cone Hamiltonian equation based on a trivial vacuum. The induced interaction is crucial for generating a splitting between pseudoscalar and vector meson masses, which we illustrate with spectrum calculations in some 1 + 1-dimensional reduced models of gauge theory.     

The real gauge hierarchy problem

We discuss the problem of generating two vastly different mass scales through spontaneous symmetry breaking. We find that to all orders in perturbation theory this can only be achieved if there is a non-trivial relation between the couplings of the theory. While this relation may come from a higher symmetry we find that this symmetry can only be broken at the low mass scale.