Precision calculations in QCD

在即将到来的欧洲核子研究中心（CERN）的大型强子对撞机（LHC）上，这是有史以来最昂贵、最雄心勃勃的粒子物理项目，我们希望了解导致所有观测到的粒子质量的电弱对称性破缺的起源和机制。大型强子对撞机的测量结果也可能揭示粒子物理学中其他悬而未决的问题，比如味道的起源、暗物质的组成和暗能量的本质，这些问题可能与电弱对称性破缺有关，也可能与之无关。基于自然性和微调等理论论据，我们认为，标准模型（SM）理论——目前是我们理解粒子动力学的基石——在TeV尺度（大型强子对撞机将探索的能量机制）周围被认为是失败的。因此，我们期望在大型强子对撞机上发现新的物理信号。这些信号可能表现为美妙的共振，也可能隐藏在大型SM后台进程后面。为了充分挖掘大型强子对撞机的发现潜力，并在后续阶段匹配大型强子对撞机升级和国际线性对撞机（ILC）的精度测量，能够以最佳精度计算信号和背景过程至关重要。我的研究的统一主题是提供理论研究，既可以匹配当前运行的对撞机的精度，也可以匹配即将到来的实验的预期精度。具体来说，我正在(I)使用一般的半数值方法，提高与LHC相关的最终状态中涉及许多粒子的过程描述的准确性，（ii）自动计算对半包含最终状态可观测值的主导修正，以推导出对部分子分布函数的新约束，（iii）开发利用重味标记的方法，这对搜索新物理很重要。（四）利用有效的理论方法将有限宽度的不稳定粒子系统地处理到更高阶，从而解决了量子场论中一个长期存在的问题。总之，我的研究旨在保证理论预测将达到尽可能高的标准，以便与大型强子对撞机和大型强子对撞机的巨大实验努力相匹配。

At the upcoming Large Hadron Collider (LHC) at CERN, the most expensive and ambitious particle physics project ever, we hope to understand the origin and mechanism of electroweak symmetry breaking which is responsible for the masses of all observed particles. The measurements at the LHC might also shed light on other open questions of particle physics such as the origin of flavour, the composition of dark matter and the nature of dark energy, questions which might or might not be related to electroweak symmetry breaking. Based on theoretical arguments like naturalness and fine-tuning, we belief that the Standard Model (SM), the theory which currently is the cornerstone of our understanding of particle dynamics, is deemed to fail around the TeV scale, the energy regime which will be explored by the LHC. We expect therefore to discover signals of new physics at the LHC. These signals might manifest themselves as beautiful resonances or they might be well hidden behind large SM background processes. In order to fully exploit the discovery potential of the LHC and, in a subsequent stage, to match the precision measurements at upgrades of the LHC and at the International Linear Collider (ILC), it is vital to be able to compute both the signals and the background processes with best accuracy. The unifying theme of my research is to provide theoretical studies that can match both the current precision of running colliders, as well as the expected accuracy of upcoming experiments. Specifically, I am working at (i) improving the accuracy of the description of processes involving many particles in the final state that are relevant for the LHC, using general, semi-numerical methods, (ii) computing automatically the dominant corrections to semi-inclusive final state observables to derive new constraints on parton distribution functions, (iii) developing methods to exploit heavy-flavour tagging which is important for searches of new physics, and (iv) using effective theory methods to treat the finite width of unstable particles systematically to higher orders, thereby solving a long-standing problem in quantum field theory. In summary, my research aims at guaranteeing that the theoretical predictions will be of the highest possible standards, in order to match the formidable experimental effort at the LHC and ILC.