Quarks in cosmos and heavy ion collisions

宇宙学和粒子物理学之间存在着基本的联系，这种联系在所有尺度上都得到了很好的确立。特别是，早期宇宙的物理学，重子生成，宇宙核合成等是基于我们对粒子物理学的现代理解。这一认识使早期的宇宙成为研究基础物理学的奇妙实验室，特别是研究理论的真空结构。相反，对高温下基础物理行为的了解，提供了大爆炸后不久发生的事情的信息。更值得注意的是，原则上，这些QCD尺度上的现象可以在RHIC（相对论重离子对撞机）、布鲁克海文国家实验室和大型强子对撞机（瑞士日内瓦）的重离子碰撞中进行实验测试，在那里可以实现这种不寻常的环境。该项目的目标是在温度T、化学势和所谓的θ参数非零的异常环境下，将QCD作为标准模型的一部分进行研究。这一知识提供了关于140亿年前宇宙大爆炸后不久在温度T=170兆电子伏时发生的事情的可靠信息。对相图（作为这些外部参数的函数）的理解是QCD中最具挑战性的问题之一。一般认为，在QCD相变过程中θ参数并没有消失。* *我的项目的第一部分是致力于用QCD的简化版本来研究所有这些难题，然而，它保留了强耦合QCD的所有相关元素，如约束，拓扑扇区的退化，非琐碎的θ依赖，以及许多其他重要方面，这些方面允许我们测试强相互作用QCD的一些迷人的特征，包括一些方面的长程顺序。相应的研究也揭示了强耦合QCD与某些拓扑有序凝聚态体系之间的深层关系。* *我项目的第二部分是将这些全新的想法应用于重离子碰撞、天体物理学和宇宙学。特别是，由于在RHIC和LHC上进行的非常有趣的实验，QCD中局部CP不变性的破坏在过去几年中一直是一个激烈研究的主题。解释观察到的不对称性的主要思想是假设有效CP违反θ参数是由于碰撞而在大范围内引起的。这导致了较大的CP奇域。为什么这些CP奇域很大？我们认为QCD中的长范围顺序是造成这种不寻常行为的原因。由于存在θ参数时夸克和反夸克之间相互作用的差异，可能会发生局部电荷分离。这种现象可以在RHIC和LHC上进行测试。RHIC和LHC的初步结果支持电荷分离效应的本质。最后，我们把同样的想法应用到宇宙学中。这些拓扑场的独特特征激发了一种建议，即宇宙中观测到的暗能量实际上可能与这种纯拓扑、非传播、远程场有关。值得注意的是，这种全新类型的能量原则上可以在实验室里通过测量所谓的拓扑卡西米尔效应来研究。

There are fundamental links between cosmology and particle physics, which have been well established at all scales. In particular, the physics of the early Universe, baryogenesis, cosmological nucleosynthesis, etc. is based on our modern understanding of particle physics. This realization has made the early Universe a marvellous laboratory for studying fundamental physics, in particular the vacuum structure of the theory. Conversely, knowledge of the behaviour of fundamental physics at high temperature gives information about what happened shortly after the Big Bang. What is more remarkable is the fact that these phenomena at the QCD scale can be, in principle, experimentally tested in heavy ion collisions at RHIC (relativistic heavy ion collider), Brookhaven National Laboratory, and at the LHC (Geneva, Switzerland) where such unusual environment can be achieved. The goal of the project is the study of QCD as part of the standard model in the unusual environment when temperature T, chemical potential and the so-called theta- parameter are non-zero. This knowledge gives a reliable information about what have happened about 14 billion years ago soon after the Big Bang at the temperature T=170 MeV. The understanding of the corresponding phase diagram (as a function of these external parameters) is one of the most challenging problems in QCD. It is generally accepted that the theta parameter was not vanishing during the QCD phase transition. * *First part of my project is devoted to study all these hard questions using a simplified version of QCD, which however preserves all the relevant elements of strongly coupled QCD such as confinement, degeneracy of topological sectors, nontrivial theta dependence, and many other important aspects which allow us to test some fascinating features of strongly interacting QCD, including some aspects of the long range order. The corresponding studies also reveal a deep relation between strongly coupled QCD and some topologically ordered condensed matter systems. * *The second part of my project is application of these fundamentally new ideas to heavy ion collisions, astrophysics and cosmology. In particular, the violation of local CP invariance in QCD has been a subject of intense studies for the last couple of years as a result of very interesting ongoing experiments at RHIC and the LHC. The main idea to explain the observed asymmetries is to assume that the effective CP violating theta parameter is induced on a large scale as a result of collision. This leads to large CP odd domains. Why are these CP odd domains large? We argue that the long range order in QCD is responsible for such an unusual behaviour. Due to the differences in interactions between quarks and antiquarks in the presence of the theta parameter the local separation of charges may take place. This phenomenon can be tested at RHIC and the LHC. Preliminary results at RHIC and the LHC support the ideas on the nature of the charge separation effect. Finally, we apply the same ideas to cosmology. The unique features of these topological fields have inspired a proposal that the observed dark energy in the universe may in fact be related to such pure topological, non- propagating, long-ranged fields. It is quite remarkable that this fundamentally new type of energy can be, in principle, studied in a laboratory by measuring the so-called topological Casimir Effect.