Quantum Field Theory: new ideas in strings, lattice and LHC physics

粒子物理学的标准模型概括了我们目前对原子基本成分和大爆炸后最早时刻物质性质的认识。然而，我们对标准模型动力学的理解受到我们解决其强相互作用部分的能力的限制，该部分被称为量子色动力学（QCD），它描述了夸克和胶子的相互作用。斯旺西集团从两个完全不同的角度来解决这个问题。首先，通过将时空连续近似为离散点格，可以在高性能计算机上模拟QCD。该小组将研究大爆炸后存在的高温和高密度极端条件下的晶格QCD，这些条件将在日内瓦欧洲核子研究中心的大型强子对撞机的高能粒子碰撞中重现，该对撞机定于2008年开始运行。然而，LHC的主要目标是发现新的物理学，它负责为所有已知的基本粒子产生质量。这种“电弱对称性破缺”是标准模型中最不为人所知的部分。这可能是由于存在一个贯穿时空的背景场，当粒子与它相互作用时，它给了粒子质量;这个场在LHC上表现为著名的“希格斯玻色子”。另一方面，质量的产生可能是由于大型强子对撞机探测到的TeV量级的新的强相互作用物理，正如与QCD类似的一类理论所描述的那样。斯旺西小组正在寻求各种方法来理解这种理论的动力学和实验特征。然而，粒子物理学家并不认为标准模型是终极理论。它是量子规范场论的一个例子，量子规范场论是一个统一量子力学、狭义相对论和物理学家通过几十年的粒子加速器实验发现的基本对称性的理论框架。更深层次的统一似乎可以用超弦来实现，超弦包含规范理论和引力，以及一种被称为“超对称性”的新型时空对称性，人们普遍认为它可以用“万物理论”来描述自然界的一切。然而，最近发现，在很多方面，规范理论和超弦可能只是看待同一基本理论的不同、互补的方式。利用这种“规范弦对偶性”是斯旺西小组的主要活动之一。这在两个方面起作用。首先，弦理论的见解可以用来阐明强相互作用超对称规范理论的性质，最终目的是从晶格理论家的另一个角度理解QCD和Technicolor的动力学。其次，规范理论的见解可以用来研究量子引力中的深层问题，例如黑洞霍金辐射的性质，以及弦理论最终如何解决大爆炸时的时空奇点问题，从而为宇宙的起源带来全新的见解。

The standard model of particle physics encapsulates our current knowledge of the fundamental constituents of atoms and the nature of matter in the earliest moments following the Big Bang. However, our understanding of the dynamics of the standard model is limited by our ability to solve its strongly-interacting sector, known as quantum chromodynamics (QCD), which describes the interactions of quarks and gluons. The Swansea group is attacking this problem from two quite different perspectives. First, by approximating the spacetime continuum as a discrete lattice of points, it is possible to simulate QCD on high performance computers. The group will study lattice QCD in the extreme conditions of high temperature and density which existed following the Big Bang and which will be recreated in high-energy particle collisions at the Large Hadron Collider at CERN in Geneva, which is due to begin operation in 2008. The primary goal of the LHC is, however, to discover the new physics which is responsible for the generation of mass for all the known elementary particles. This `electroweak symmetry breaking' is the least understood part of the standard model. It may be due to the existence of a background field permeating spacetime, which gives mass to particles as they interact with it; this field would manifest itself at the LHC as the famous `Higgs boson'. On the other hand, mass generation may be due to new strong interaction physics at the TeV scale probed by the LHC, as described by a class of theories known in analogy with QCD as `technicolor'. The Swansea group is pursuing a variety of approaches to understand the dynamics and experimental signatures of this type of theory. Particle physicists do not, however, believe that the standard model is the ultimate theory. It is an example of a quantum gauge field theory, a theoretical framework which unifies quantum mechanics, special relativity and the fundamental symmetries which physicists have discovered through decades of experiments with particle accelerators. A deeper unification appears possible with superstrings, which contain both gauge theories and gravity together with a new type of spacetime symmetry known as `supersymmetry', and are widely believed to describe all of nature in a `Theory of Everything'. However, it has recently been discovered that in many ways gauge theories and superstrings may be simply different, complementary ways of viewing the same fundamental theory. Exploiting this `gauge-string duality' is one of the main activities of the Swansea group. This works in two ways. First, insights from string theory can be used to elucidate properties of strongly-interacting supersymmetric gauge theories with the ultimate aim of understanding the dynamics of QCD and technicolor from an alternative perspective to the lattice theorists. Second, insights from gauge theories can be used to study deep problems in quantum gravity, such as the nature of Hawking radiation from black holes and eventually how string theory may resolve the problem of the spacetime singularity at the Big Bang, throwing a completely new light on the origin of the universe.