Particles, Fields and Extended Objects

剑桥大学理论高能物理小组的STFC研究项目侧重于对撞机现象学、量子场论、弦理论和引力的基本问题，以及分析一类被称为介子的强相互作用粒子。我们正在分析和解释来自欧洲核子研究中心的大型强子对撞机数据，以做各种事情：寻找新粒子或力的迹象，为它们制定搜索和测量策略，或者对各种理论进行高精度预测。标准模型是粒子物理学的当前模型，它被广泛接受、验证和测量。它的大多数预测都与对撞机的数据吻合得很好。然而，它留下了许多问题没有回答：为什么希格斯玻色子这么轻（理论预测它应该是10^15倍重）？什么是暗物质？为什么宇宙是由物质而不是反物质构成的？新物理学的模型解释了其中的一些或全部，并且通常预测新的粒子。找到这些（或排除它们）是检验这些理论的首要任务。大型强子对撞机刚刚升级到它的最高能量，13 TeV，这意味着可能会发现以前从未见过的更重的粒子。最近的数据中出现了令人兴奋的意想不到的“颠簸”：例如，太多的光粒子（光子）似乎是从质子碰撞中产生的，其能量相当于750个质子质量。如果它被证实，这将是一个新粒子的信号，它会衰减为两个光子，问题是：这在哪里合适，它意味着什么？我们正在积极解决这些问题。量子场论对已知的粒子相互作用提供了非常成功的描述。然而，当相互作用很强时，需要特殊的技术来进行预测。我们将开发各种技术来改进这些，并提供对潜在动力学的理解。弦理论是一个数学上非常丰富的结构，旨在描述引力。它的一种变体甚至可能是在自然界中观察到的所有粒子之间相互作用的基础。这些微小的环路表现得像粒子，除非有人以我们目前实验无法达到的高能量探测它们。我们的一些研究考察了这些理论数学背后的丰富结构：结果表明，散射两个粒子和散射三个粒子在相互作用概率之间有严格的关系。有时，通过将一个弦理论映射到另一个弦理论，这样的事实更容易理解，因为另一个弦理论具有不同的耦合强度和不同数量的时空维度。这些“二象性”帮助我们找出弦理论的真相和深层联系。我们将研究它们在相互作用概率之间的关系中的作用。我们正在分析黑洞理论的不稳定性，这取决于维度的数量和底层时空的弯曲程度。有些粒子是较小粒子的强束缚态，比如b介子。为此，建立了复杂的计算机程序，将空间和时间分解成点网格，并使用该网格上的随机数模拟亚核相互作用的量子涨落。为了使计算机上得到的数字与实验数据相符，必须进行分析计算。我们将发展这些计算，并执行新的计算，以便数据可以用于提取各种夸克（例如，上夸克和b夸克）混合的水平。这有助于准确描述一种无法解释的现象：夸克混合的有趣模式是如何产生的。这些计算也有助于从实验数据中提取物质和反物质之间的差异。

The STFC research programme of the Theoretical High Energy Physics Group atCambridge University is focused on the fundamental problems of colliderphenomenology, quantum field theory, string theory and gravity, and analysingclass of strongly interacting particles called mesons.We are analysing and interpreting Large Hadron Collider data from CERN to dovarious things: looking for signs of new particles or forces, developingsearch and measurement strategies for them, or making high precisionpredictions of various theories. The Standard Model is the current model ofparticle physics that is well accepted, verified and measured. Most of itspredictions agree well with collider data. However, it leaves many questionsunanswered: why is the Higgs boson so light (the theory predicts it should be10^15 times heavier)? what is dark matter? how come the universe is made ofmatter and not anti-matter? Models of new physics explain some or all ofthese, and typically predict new particles. Finding these (or ruling them out)is a priority in order to test such theories. The Large Hadron Collider hasjust upgraded to its highest energy, 13 TeV, which means that heavierparticles may be found that haven't been seen before. There have been excitingunexpected "bumps" in data recently: for example too many pairs of particlesof light (photons) seem to be coming out of the proton proton collisions withan energy equivalent to 750 proton masses. If it is verified, this would be asignal of a new particle which decays to two photons, and the question is:where does this fit and what does it mean? We are actively working on suchquestions. Quantum field theory provides a very successful description of known particleinteractions. However, special techniques are required to get predictions whenthe interactions are strong. We shall be developing various techniques toimprove these, and to provide understanding of the underlying dynamics.String theory is an extraordinarily mathematically rich structure, thatpurports to describe gravity. One variant of it may also even underlie all ofthe interactions between particles that are observed in nature. The tiny loopsbehave like particles unless one probes them at energies that are far too highfor us to reach in current experiments. Some of our research examines the richstructure behind the mathematics of these theories: it turns out thatscattering two particles and scattering three particles have strict relationsbetween the interaction probabilities. Sometimes, truths such as these areeasier understood by mapping one string theory to another one, which has adifferent coupling strength and a different number of space-timedimensions. These "dualities" help us winkle out truths anddeep connections in string theory. We shall be investigating their role in therelations between interaction probabilities. We are analysing instabilities in theories of black holes, depending on thenumber of dimensions and how bent the underlying space-time is. Some particlesare strongly bound states of smaller ones, such as B-mesons. For these, sophisticated computer programs arebuilt which break space and time up into a grid of points, and the quantumfluctuations of the sub-nuclear interactions are simulated using randomnumbers on this lattice. Analytic calculations must be done to match thenumbers obtained on the computer to experimental data. We shall develop thesecalculations, and perform new ones so that data can be used to extract thelevel to which various quarks (for example, the up quark and the b-quark)mix. This helps provide an accurate description of an unexplained phenomenon:how the funny pattern of quark mixing comes about. These calculations alsohelp the extraction of the difference between matter and anti-matter fromexperimental data.