Theoretical Studies of Elementary Particles

我们的最终目标是了解物质的本质和驱动宇宙的最基本的过程。我们宇宙最耐人寻味的特征之一是，我们似乎能够很好地描述发生的许多事情--使用一套以数学模型的形式写下的定律。艾萨克·牛顿证明，这可以用肉眼可见的物体来完成，现代理论家延续了极端事件必须产生的粒子的传统，无论是宇宙还是地球上的粒子，在像欧洲核子研究中心的大型强子对撞机(LHC)这样的加速器上。这项拟议的研究将解决当今粒子理论中的主要问题。我们建议的第一部分是改进对大型强子对撞机碰撞中主导粒子产生的强相互作用(QCD)影响的预测。这些碰撞产生了大量的已知粒子，这些粒子必须被过滤掉，这样才能看到表明新粒子存在的罕见事件。希格斯玻色子的发现依赖于这样的计算；更多新粒子的发现，以及对其性质的有效分析，将取决于以更高的精度进行这些计算。强、弱和电磁相互作用的标准模型精确地描述了大多数粒子物理，但它有缺陷。它没有解释暗物质，为什么弱相互作用尺度相对较轻，也没有解释为什么有三代夸克和轻子，它也不包含引力。我们的研究将探索可能弥补这些缺陷的模型，并确定哪些实验测试将对他们预测的新的“超越标准模型(BSM)”物理敏感。我们将研究超对称场理论和具有额外空间维度的模型，以确定它们是否包含可行的暗物质候选者，而不引入其他与实验不相容的新物理。超弦理论是将标准模型与引力统一起来的一个很有前途的候选者。然而，一般来说，它们包含大量自然界中没有观察到的粒子；我们将继续我们的计划，以找到与标准模型一致的粒子，并首次计算出详细比较轻粒子质量与实验所需的汤川耦合。大型强子对撞机还被用来碰撞产生夸克-胶子等离子体的重离子。理解这种新的物质状态的特征是具有挑战性的。它很快达到热平衡，并极大地影响通过它的高能粒子的行为。所谓的规范弦对偶技术可以解决其中的一些问题，但并不严格适用于真正的QCD。我们建议发展一种将这种方法与其他技术相结合的复合描述来理解真实夸克-胶子等离子体的性质。标准模型的扩展通常包含新的粒子，这些粒子不能在大型强子对撞机上直接探测到，但会影响天体物理和宇宙过程，如暴胀和原始引力波的产生。一个例子是所谓的ALP，它是在大多数弦理论中自然产生的，它的存在将在天体物理X射线数据中看到。我们建议的一个重要部分是详细建立来自这种物理的信号，以便我们可以优化在观测数据中检测它们的策略。相比之下，量子引力还没有被足够好地理解为反对测量的张力理论，所以我们将开发一些方法，在因果动力学三角剖分等模型中计算宇宙的大尺度属性，以确定它们是否是描述量子重力的可信候选者。

Our ultimate aim is to understand the nature of matter and the most basic processes that drive the universe. One of the most intriguing features of our universe is that we seem to be able to describe much of what happens very well 'theoretically' - using a a set of laws that are written down in the form of a mathematical 'model'. Isaac Newton showed this could be done with objects visible to the naked eye and modern day theorists continue the tradition for particles that have to be created by extreme events, be they cosmic or terrestrial at accelerators like the Large Hadron Collider (LHC) at CERN. The proposed research will address today's major issues in particle theory.The first part of our proposal is to improve predictions of the effects of the strong interactions (QCD) that dominate the production of particles in collisions at the LHC. These collisions create showers of large numbers of known particles which have to be filtered out so that the rare events indicating the presence of a new particle become visible. The discovery of the Higgs boson depended on such calculations; the discovery of further new particles, and the efficient analysis of their properties, will depend on doing those calculations to even higher precision.The Standard Model of the strong, weak and electromagnetic interactions describes most of particle physics with exquisite precision but it has defects. It does not explain dark matter, why the weak interaction scale is relatively light or why there are three generations of quarks and leptons, and it does not contain gravity. Our research will explore models that might remedy these defects and determine what experimental tests would be sensitive to the new 'beyond the Standard Model (BSM)' physics they predict. We will examine supersymmetric field theories, and models with additional space dimensions, to establish whether they contain viable candidates for dark matter without introducing other new physics incompatible with experiment. Superstring theories are a promising candidate for unifying the Standard Model with gravity. However generally they contain an abundance of particles not observed in nature; we will continue our programme to find those consistent with the Standard Model and for the first time calculate the Yukawa couplings that are needed for detailed comparison of light particle masses with experiment. The LHC is also used to collide heavy ions producing a quark-gluon plasma. Understanding the features of this new state of matter is challenging. It reaches thermal equilibrium very quickly and affects non-trivially the behaviour of energetic particles passing through it. The so-called gauge-string duality technique can attack some of these problems but does not apply strictly to real QCD. We propose to develop a composite description that combines this method with other techniques to understand the properties of the real quark-gluon plasma.Extensions of the Standard Model usually contain new particles that cannot be detected directly at the LHC but affect astrophysical and cosmological processes such as inflation and the generation of primordial gravitational waves. An example is the so-called ALP which arises naturally in most string theories and whose presence would be seen in astrophysical X-ray data. An important part of our proposal is to establish in detail the signals from such physics so that we can optimize strategies for detecting them in observational data. In contrast quantum gravity is not yet sufficiently well understood to tension theory against measurement so we will develop methods of computing the large scale properties of the universes in models such as causal dynamical triangulations to determine whether they are plausible candidates to describe quantum gravity.