暗物质理论研究

正粒子物理主要研究自然界基本粒子以及它们之间的相互作用。考虑电弱对称性破缺之前的粒子物理标准模型和引力,我们知道自然界存在四种基本相互作用:强、弱、超荷和引力相互作用。我们用对称性描述基本粒子和它们之间的相互作用,如庞加莱代数的两个Casimir算子描述了粒子的质量和自旋,引力相互作用是用广义坐标变换(或数学上说微分同胚变换)下的不变性来描述,强、弱和超荷相互作用是用规范理论来描述,其相应的规范群     

物质结构在夸克-轻子层次上的动力学规律和研究发展趋势

文章综述了粒子物理中标准模型理论的历史发展、面临挑战以及未来的发展趋势.目前阶段物质结构最小组成单元是夸克和轻子,量子色动力学是描述夸克-胶子之间强相互作用的基本理论,它具有渐近自由和夸克禁闭的特点.量子色动力学和电弱统一理论一起构成粒子物理中标准模型理论.标准模型理论成功同时也面临两大挑战:对称性破缺的本质和夸克禁闭难题,这意味着标准模型理论需要发展和突破.人们期望粒子物理学、天文学和宇宙学交叉发展联手解决物质结构和早期宇宙研究中面临的难题,最终揭示超出标准模型的新物理规律.     

中子有无电偶极矩?

测量中子电偶极矩的新方法更好地约束了关于宇宙早期对称性破缺的理论。虽然中子整体上是电中性,但它内部电荷的分布也可能并非对称,定量上用电偶极矩(EDM)来描述这种不对称性。有些试图拓展粒子物理学标准模型的理论预言中子EDM非零,而最近一个国际合作组给出了新的测量上限。他们通过测量一团中子跟电磁场的相互作用来得到这一限制。该发现有望帮助理论学家更好地解释宇宙正反物质的不对称。     

基本粒子和相互作用的标准模型简介

本文对粒子物理理论中的粒子及其相互作用做了较为全面的综述。笔者尽可能不用物理公式来说明相关物理规律和思想,而是通过对称性与对称性破缺,对粒子物理理论所涉及的量子力学的解释以及对组成物质基元的理解进行描述。本文也对目前标准模型存在的问题进行了讨论。     

粲夸克的电荷—宇称非对称性

<正>在基本粒子物理的标准模型中,电荷—宇称(CP)对称性是严格遵守的,但在夸克之间的弱相互作用中是违反的。理论认为,在弱相互作用中CP对称性的破坏,可能使早期宇宙中产生的物质比反物质多。在量子物理体系中,CP是一个     

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.     

反物质和暗能量

 上个世纪,人类在探索宇宙奥秘和物质基本结构及其相互作用的道路上取得了辉煌的成就,建立了描述微观世界的粒子物理标准模型和描述宇观世界的大爆炸宇宙学标准模型。粒子宇宙学将微观世界和宇观世界、粒子物理学和天文学结合起来,研究早期宇宙这一极端条件下的物理规律,探讨基本粒子的相互作用的统一。近代宇宙学研究表明,在宇宙演化过程中经历了暴涨(Inflation)阶段。基于粒子物理的标量场理论,暴涨宇宙学不仅为经典大爆炸宇宙模型中的初始条件和疑难给予了答案,而且提供了一个描述宇宙大尺度结构成因的合理理论,并为近年观测所支持。     

受限于对称性破缺狭缝间氢键流体的相平衡研究

利用密度泛函理论并结合改进的基本度量理论研究了受限于对称性破缺狭缝间氢键流体的相平衡. 首先根据氢键流体的吸附-脱附等温线及相应巨势获得不同条件下氢键流体的相图. 进一步讨论了氢键作用、狭缝间距、狭缝与流体分子间相互作用及对称性破缺程度等因素对氢键流体相平衡的影响. 结果表明, 由于狭缝与流体分子及流体分子间的相互作用存在竞争, 使得受限于对称性破缺条件下的氢键流体呈现更为复杂的相态特征.     

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     

中国科学有发现电荷-宇称-时间反演对称性破缺迹象

 一个由中国科学院高能物理所和中国科学院国家天文台科研人员组成的研究小组,通过一种用宇宙微波背景辐射偏振检验CPT对称性的新方法,取得了重要成果：发现电荷-宇称-时间反演(CPT)对称性破缺迹象。据介绍,现代宇宙学的研究表明,宇宙中存在着一种神秘的暗能量。如果这种暗能量随宇宙的膨胀而演化,并与电磁场有某种相互作用(陈省身·西蒙斯相互作用),就有可能破坏CPT定理成立的条件,这会使光子的偏振方向传播中发生改变。宇宙微波背景辐射光子是我们能看到的来自宇宙最遥远的光子,研究小组设计出了一种用宇宙微波背景辐射偏振检验CPT对称性的新方法,使检测灵敏度大大提高。在用这种方法分析了美国WMAP卫星和Boom     

原子核层次的手征对称性

对称性及其破缺是基本的科学问题。手征对称性在自然界中广泛存在,大至星系旋臂、行星自转,小到矿物晶体、有机分子、基本粒子,都与手征对称性密切相关。原子核层次的手征对称性概念于1997年提出,随后成为核物理研究的热点问题。目前,实验上已经在核素图上的80,100,130和190质量核区发现了30多例可能具有手征对称性的原子核。简要介绍原子核中的手征对称性概念;手性原子核的预言、识别以及实验验证;并通过展示手性原子核结构的多样性（M_χD）,回顾了理论和实验研究进展;介绍最新发现的原子核中手性和空间反射对称性的联立自发破缺,对未来手性原子核研究的前景进行了展望。Symmetry and its breaking are basic scientific problems. Chiral symmetries are common in nature, for example, the macroscopic spiral arms of galaxies and the rotation of planets; the microscopic spirals of the mineral crystalline, the organic molecules and the elementary particles. The concept of chirality in atomic nuclei was first proposed in 1997. Since then many efforts have been made to understand chiral symmetry and its spontaneous breaking in atomic nuclei. Up to now, more than 30 candidates of chiral nuclei have been reported in the 80, 100, 130, and 190 mass regions. The concept of the chirality in atomic nuclei, the prediction, the signal, and the experimental verification of the chiral nuclei are briefly introduced; the recent theoretical and experimental progress are reviewed, in particular the existence of multiple chiral doublets (M_χD), i.e., more than one pair of chiral doublet bands in one single nucleus; the simultaneous spontaneous breaking of chiral and reflection symmetry in the newly observed atomic nuclei is introduced, together with a prospect on the future study on nuclear chiral symmetry.     

Some Quantum Symmetries and Their Breaking I

We give an account of the genesis of the gauge groups of the standard model plus gravity and their concomitant interaction terms ab initio from a consideration of the quantization of certain classical discrete symmetries. We indicate how the resulting symmetries may be gauged upon a semi-quantized non manifold-like model of spacetime. This model is briefly introduced and some of its pre- or quantum geometry is developed from first principles. The formalism leads to a view of gauge interaction that admits an apparently new form of symmetry breaking that accounts, among other things, for the chiral breaking of the weak interaction. (A sequel will give an account of a range of mechanisms to break other symmetries arising in the standard model, and will consider some of their experimental consequences.)     

The breaking of quantum double symmetries by defect condensation

In this paper, we study the phenomenon of Hopf or more specifically quantum double symmetry breaking. We devise a criterion for this type of symmetry breaking which is more general than the one originally proposed in F.A. Bais, B.J. Schroers, J.K. Slingerland [Broken quantum symmetry and confinement phases in planar physics, Phys. Rev. Lett. 89 (2002) 181601]; Hopf symmetry breaking and confinement in (2+1)-dimensional gauge theory, JHEP 05 (2003) 068], and therefore extends the number of possible breaking patterns that can be described consistently. We start by recalling why the extended symmetry notion of quantum double algebras is an optimal tool when analyzing a wide variety of two-dimensional physical systems including quantum fluids, crystals and liquid crystals. The power of this approach stems from the fact that one may characterize both ordinary and topological modes as representations of a single (generally nonabelian) Hopf symmetry. In principle a full classification of defect mediated as well as ordinary symmetry breaking patterns and subsequent confinement phenomena can be given. The formalism applies equally well to systems exhibiting global, local, internal and/or external (i.e. spatial) symmetries. The subtle differences in interpretation for the various situations are pointed out. We show that the Hopf symmetry breaking formalism reproduces the known results for ordinary (electric) condensates, and we derive formulae for defect (magnetic) condensates which also involve the phenomenon of symmetry restoration. These results are applied in two papers which will be published in parallel [C.J.M. Mathy, F.A. Bais, Nematic phases and the breaking of double symmetries, arXiv:cond-mat/0602109, 2006; F.A. Bais, C.J.M. Mathy, Defect mediated melting and the breaking of quantum double symmetries, arXiv:cond-mat/0602101, 2006].     

Breakdown of Landau Fermi liquid theory: Restrictions on the degrees of freedom of quantum electrons

One challenge in contemporary condensed matter physics is to understand unconventional electronic physics beyond the paradigm of Landau Fermi-liquid theory. Here, we present a perspective that posits that most such examples of unconventional electronic physics stem from restrictions on the degrees of freedom of quantum electrons in Landau Fermi liquids. Since the degrees of freedom are deeply connected to the system’s symmetries and topology, these restrictions can thus be realized by external constraints or by interaction-driven processes via the following mechanisms: (i) symmetry breaking, (ii) new emergent symmetries, and (iii) nontrivial topology. Various examples of unconventional electronic physics beyond the reach of traditional Landau Fermi liquid theory are extensively investigated from this point of view. Our perspective yields basic pathways to study the breakdown of Landau Fermi liquids and also provides a guiding principle in the search for novel electronic systems and devices.     

The Phase Structure of a Generalized Gross–Neveu Model in (2+1)-Dimensional Space–Time

The phase structure of a (2+1)-dimensional Gross–Neveu model with four different channels of fermion–antifermion interaction, and, correspondingly, four different coupling constants, is studied. It is shown that the model describes five different phases of the interaction of planar fermions in which either spatial parity or chiral symmetry can be broken. The existence of a phase that is characterized by simultaneous spontaneous breaking of both these symmetries that was not observed earlier in such models is demonstrated.     

SOS: 对称操作相似原理

凝聚态物理学往往为对称性所支配。自发对称性破缺将导致相变,而且许多可观测量或物 理现象都与破缺的对称性有关,如铁电极化、铁磁磁化、旋光性（包括法拉第旋转和磁光克尔旋 转）、二次谐波发生、光伏效应、非互易性、霍尔效应型输运以及多铁性。在这里,我们提出以 下观点：从对称性破缺的角度来看,当构成量（如自旋排列、晶格畸变,或处于外场以及其他环 境中等）或测量方式（如光学探测,或处于不同极性态中电子和其它粒子探测,或对体极化[磁 化] 等的测量）遵循对称操作相似(symmetry operational similarity, SOS) 原理时,我们便可以 观测到某些特定的物理现象。这种SOS原理提供了一种在复杂材料中用简洁而清晰的物理图像描 述非直观物理现象的途径。反之,也可以用于甄别具有潜在需求特性的新材料,或发现已知材料 中新的物理现象。     

Stabilizing the axion by discrete gauge symmetries

The axion solution to the strong CP problem makes use of a global Peccei–Quinn U(1) symmetry which is susceptible to violations from quantum gravitational effects. We show how discrete gauge symmetries can protect the axion from such violations. PQ symmetry emerges as an approximate global symmetry from discrete gauge symmetries. Simple models based on Z_N symmetries with N=11,12, etc., are presented realizing the DFSZ axion and the KSVZ axion. The discrete gauge anomalies are canceled by a discrete version of the Green–Schwarz mechanism. In the supersymmetric extension our models provide a natural link between the SUSY breaking scale, the axion scale, and the SUSY-preserving μ term.     

Transition to deformed shapes as a nuclear Jahn-Teller effect

The Jahn-Teller effect is well known in molecular physics as an interplay between degenerate electronic states and a molecular vibration, giving rise to a spontaneous breaking of a molecular symmetry. We translate the concept of the Jahn-Teller effect to nuclear physics and discuss nuclear collective motion and deformation from that point of view. It becomes transparent that the well-known surface quadrupole motion, with its tendency to stable deformations, can be understood as a nuclear Jahn-Teller mode emerging from the interaction between degenerate nucleon states and giant resonance vibrations. The axial symmetry may break down further to non-axial or to reflection asymmetry shapes by the same mechanism.     

About the non vanishing of boundary terms in correlation functions as origin of phase transitions. A microscopic proof of a Goldstone theorem in classical statistical mechanics

We give a general microscopic proof that the well known Goldstone theorem connected with spontaneous symmetry breaking in quantum statistical mechanics and quantum field theory has a counterpart in classical statistical mechanics. Our approach is mainly based on the replacement of commutators by Poisson brackets as infinitesimal generators of symmetries and on the Fourier transformed version of the so called Kubo-Martin-Schwinger property of equilibrium states. Especially we show that the phase transition is related to the non vanishing of certain boundary contributions in Poisson brackets which from the naive point of view should vanish.