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Investigations in Particle Physics Theory

粒子物理理论研究

基本信息

批准号：
ST/J000434/1
负责人：
Nicholas Stephen Manton
金额：
$ 162.53万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FJ000434%2F1
关键词：
Investigations Particle Physics Theory

项目摘要

The Cambridge Particle Physics Theory group has broad interests including searching for new particles at the Large Hadron Collider (LHC) at CERN, understanding string theory, and studying the different types of particles that occur in quantum field theories. One of our members is string theorist Michael Green, successor to Stephen Hawking as Lucasian Professor. The group has devoted much effort to developing accurate models of the quark structure inside the protons that collide at LHC, and predicting the outcome of the proton-proton collisions. This work is vital if the signature events involving new particles are to be recognised in the experiments. We will analyse and interpret results from LHC that suggest new particles, for example events where energy and momentum is carried away by unseen, electrically neutral particles. We are particularly interested in searches for the Higgs particle, whose mass appears to be in the range that LHC can reach. A striking signal of a Higgs particle is its frequent decay to two bottom (b) quarks, and it would decay even more frequently into two top (t) quarks (the heaviest type) if it had enough mass. Other aspects of heavy quark physics are also interesting and we are using supercomputers to calculate as accurately as possible the decay rates of particles that contain b quarks. Discrepancy with experiment could reveal new physics. Another kind of new particle that many theorists expect to see is a 'supersymmetric' partner of one of the particles familiar to us. Supersymmetry is a revolutionary idea for unifying particles of different types. It cannot be an exact symmetry of nature and there are many models for how supersymmetry may be only approximately true. We have developed statistical tools to distinguish among them, to be applied as LHC produces data at ever increasing energies. The reason for believing in supersymmetry is that it makes some of our most powerful theories, both quantum field theories and string theory, mathematically more consistent. Field theories present some mathematical difficulties, which get worse if there are extra dimensions of space beyond the usual three. String theory avoids some of these difficulties, and is consistent in ten spacetime dimensions, provided it is supersymmetric. It has the right structure to describe families of particles similar to those we know, and to make gravity theory consistent with quantum mechanical effects, a combined success not achieved in any other way. We are still testing in detail whether string theory avoids all the difficulties which are troublesome, though not fatal, for field theories. We will also explore the remarkable gauge/gravity correspondence, derived from string theory. This allows us to study phenomena in the physical world in which ordinary gravity plays a negligible role, like the quark-gluon plasma state, the structure of atomic nuclei, and certain effects in exotic superconductors, by carrying out gravity calculations in unphysical extra dimensions. But this is currently controversial, partly because the rigorous results justifying it rely on exact supersymmetry. We will be trying to understand how widely it can be applied, as well as looking for potential new applications. Some of our work involves solving equations in the classical approximation to quantum field theory, analogous to solving Maxwell's equations in optics rather than studying many photons. This is mathematically very interesting. Examples of solutions are various types of vortices, and the Skyrmions that were observed recently in exotic magnets. Skyrme's original idea was to model nuclei by Skyrmions. It gives a picture of a nucleus intermediate between a cluster of rigid, spherical protons and neutrons, and a structureless liquid drop. We will test the Skyrme picture through its predictions for the force between Helium-4 nuclei (alpha particles), and for the spectra of energy levels of excited nuclei.

剑桥粒子物理理论小组兴趣广泛，包括在欧洲核子研究中心的大型强子对撞机 (LHC) 中寻找新粒子、理解弦理论以及研究量子场论中出现的不同类型的粒子。我们的成员之一是弦理论家迈克尔·格林，他是斯蒂芬·霍金卢卡斯教授的继任者。该小组投入了大量精力来开发在大型强子对撞机上碰撞的质子内部夸克结构的精确模型，并预测质子-质子碰撞的结果。如果要在实验中识别涉及新粒子的特征事件，这项工作至关重要。我们将分析和解释大型强子对撞机的结果，这些结果表明了新的粒子，例如能量和动量被看不见的电中性粒子带走的事件。我们对寻找希格斯粒子特别感兴趣，其质量似乎在大型强子对撞机可以达到的范围内。希格斯粒子的一个显着信号是它频繁衰变成两个底夸克 (b)，如果它有足够的质量，它会更频繁地衰变成两个顶夸克 (t)（最重的类型）。重夸克物理学的其他方面也很有趣，我们正在使用超级计算机来尽可能准确地计算包含 b 夸克的粒子的衰变率。与实验的差异可能会揭示新的物理学。许多理论学家期望看到的另一种新粒子是我们熟悉的粒子之一的“超对称”伙伴。超对称是统一不同类型粒子的革命性想法。它不可能是自然界的精确对称性，并且有许多模型可以解释超对称性如何只能近似真实。我们开发了统计工具来区分它们，并在大型强子对撞机以不断增加的能量产生数据时应用。相信超对称性的原因是它使我们一些最强大的理论，无论是量子场论还是弦理论，在数学上更加一致。场论提出了一些数学难题，如果空间存在超出通常三个维度的额外维度，情况会变得更糟。弦理论避免了其中一些困难，并且在十个时空维度上是一致的，只要它是超对称的。它具有正确的结构来描述与我们已知的粒子类似的粒子族，并使引力理论与量子力学效应相一致，这是任何其他方式都无法取得的综合成功。我们仍在详细测试弦理论是否避免了对场论来说虽然不是致命但麻烦的所有困难。我们还将探索源自弦理论的非凡的规范/重力对应关系。这使我们能够通过在非物理额外维度中进行重力计算来研究物理世界中的现象，其中普通重力起着可忽略不计的作用，例如夸克-胶子等离子体态、原子核的结构以及奇异超导体中的某些效应。但这目前存在争议，部分原因是证明其合理性的严格结果依赖于精确的超对称性。我们将尝试了解它的应用范围，并寻找潜在的新应用。我们的一些工作涉及求解量子场论的经典近似方程，类似于求解光学中的麦克斯韦方程，而不是研究许多光子。这在数学上非常有趣。解决方案的例子是各种类型的涡流，以及最近在奇异磁体中观察到的斯格明子。 Skyrme 最初的想法是通过 Skyrmions 来模拟原子核。它给出了介于刚性球形质子和中子簇之间的原子核和无结构液滴的图片。我们将通过预测 Helium-4 原子核（α 粒子）之间的力以及激发核的能级光谱来测试 Skyrme 图。