Particles, Fields and Spacetime

粒子物理学即将进入一个新的关键阶段。欧洲核子研究中心的大型强子对撞机将使我们能够从实验上检验许多低于粒子物理标准模型的理论概念，并搜索被认为统一了物理定律的更深层次的结构。量子场论是表达标准模型的数学语言，它将粒子视为点状物体。在我们生活的四维世界中，只有特定类型的量子场论，即规范理论，是一致的。这些理论包括描述光与电荷相互作用的电动力学理论，也是这些理论的推广。为了能够解释实验的结果，我们需要能够解决规范理论，至少是近似的。这是一个困难的问题，但由于最初在完全不同的背景下为解决非常不同的理论而发展的思想的汇聚，最近取得了非常显著的进展。该项目的一个主要推动力将是进一步推进这一调查路线，以便能够更充分地了解规范理论并能够计算其性质。爱因斯坦的广义相对论所描述的大尺度物质是由引力支配的。它支配着行星、恒星、星系的运动，以及宇宙本身的演化。统一广义相对论和粒子物理标准模型是理论物理面临的最大挑战。虽然不是普遍的，但人们普遍认为弦理论提供了这样的统一。弦理论用扩展的物体取代了量子场论中的点状粒子，扩展物体的不同振动模式解释了不同种类的基本粒子。正是这种信念导致了人们的期望，即超对称性是所有现实弦理论的属性，在自然界中发挥着作用，很可能在大型强子对撞机上被发现。展示大自然是如何设法隐藏这一属性的，是该项目的另一个部分。弦理论还导致了不同类型的物理理论之间的许多意想不到的关系，最明显的是在ADS/CFT通信中，它表明了某些引力理论和相应的规范理论之间的等价性，使我们能够通过研究一种理论中的较简单的理论来解决另一种理论中的难题。我们将利用它来研究重力中的问题，否则这些问题将是难以解决的，并通过重力对不同地区的强耦合物理过程进行建模。我们还将使用另一种方法来研究强子，这种方法特别适合描述束缚在原子核甚至中子星上的大量强子。这是基于有效场理论，例如Skyrme模型，我们将使用计算机对该模型进行数值研究。作为一种量子引力弦理论，它对宇宙学有很多启示，特别是它们承认，我们所看到的物理宇宙只是一个被称为膜的低维子空间，在更高维度的空间中运动。我们将继续寻找直接的实验和观测签名，以测试这一情景。

Particle Physics is about to enter a new and crucial phase. The Large Hadron Collider at CERN will enable us to examine experimentally many of the theoretical concepts that underly the standard model of particle physics and search for the deeper structures that are believed to unify the laws of physics. Quantum field theory is the mathematical language in which the standard model is expressed, and it treats particles as point-like objects. Only certain kinds of quantum field theories, known as gauge theories, are consistent in the four dimensional world we live in. These include, and are generalisations of, the theory of electrodynamics that describes light interacting with electric charge. To be able to interpret the results of experiments we need to be able to solve gauge theories, at least approximately. This is a hard problem, but one in which there has recently been very remarkable progress due to a convergence of ideas originally developed in quite disparate contexts for solving very different kinds of theories. A major thrust of the project will be to push this line of enquiry further so as to be able to more fully understand gauge theories and be able to compute their properties. Matter at large scales is dominated by gravity which is described by Einstein's theory of General Relativity. This governs the motion of planets, stars, galaxies, and the evolution of the Universe itself. Uniting General Relativity and the standard model of particle physics is the most important challenge facing theoretical physics. It is widely, though not universally, believed that string theory provides such a unification. String theory replaces the point-like particles of quantum field theory with extended objects whose different vibrational modes account for the different species of fundamental particles. It is this belief that leads to the expectation that supersymmetry, a property of all realistic string theories, plays a role in nature, and may well be discovered at the LHC. Showing how nature contrives to hide this property is another part of the project. String theory has also lead to many unexpected relations between different kinds of physical theories, most notably in the AdS/CFT correspondence which states equivalences between certain gravity theories and corresponding gauge theories, enabling us to solve difficult problems in one theory by studying simper ones in the other. We will use this to study problems in gravity that would otherwise be intractable and also model strongly coupled physical processes in diverse areas by gravity. We will also use another method for studying hadrons that is particularly appropriate to describing large numbers of them bound into nuclei or even neutron stars. This is based on effective field theories such as the Skyrme model which we will investigate numerically using computers. Being a theory of quantum gravity strings have many implications for cosmology, in particular they admit the possibility that what we see as the physical universe is only a low dimensional subspace called a brane, moving in a space of higher dimensions. We will continue the quest to find direct experimental and observational signatures that will test this scenario.