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的了解，以及宇宙大爆炸后最初时刻物质的本质。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，即量子色动力学（QCD），它描述了夸克和胶子的相互作用。斯旺西大学的研究小组正从两个截然不同的角度来解决这个问题。首先，通过将时空连续体近似为点的离散晶格，可以在高性能计算机上模拟QCD。该小组将在宇宙大爆炸之后的高温和高密度的极端条件下研究晶格QCD，并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，该对撞机将于2008年开始运行。然而，大型强子对撞机的主要目标是发现所有已知基本粒子产生质量的新物理原理。这种“电弱对称性破缺”是标准模型中最难以理解的部分。这可能是由于穿越时空的背景场的存在，当粒子与背景场相互作用时，背景场赋予粒子质量；这个场将在大型强子对撞机中表现为著名的“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在TeV尺度上探测到的新的强相互作用物理，正如一类被称为“彩色”的理论所描述的那样，与QCD类似。斯旺西小组正在寻求各种方法来理解这类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就是终极理论。这是量子规范场论的一个例子，量子规范场论是一个理论框架，它统一了量子力学、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。超弦包含规范理论和引力，以及一种被称为“超对称”的新型时空对称。人们普遍认为，超弦可以在“万物理论”中描述自然界的一切。然而，最近人们发现，在许多方面，规范理论和超弦可能只是观察同一基本理论的不同、互补的方式。利用这种“量规弦二象性”是斯旺西小组的主要活动之一。这有两种工作方式。首先，来自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，其最终目的是从另一个角度来理解QCD和彩色的动力学，而不是从晶格理论家的角度。其次，规范理论的见解可以用于研究量子引力的深层问题，比如黑洞霍金辐射的本质，以及最终弦理论如何解决大爆炸时的时空奇点问题，从而为宇宙的起源提供一个全新的视角。

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.