Precision calculations for loop-induced Higgs-boson production and decay processes

在过去十年中，粒子物理学最重要的成就之一是在大型强子对撞机（LHC）实验中发现了希格斯玻色子。为了精确地确定它的性质，这种新粒子现在是理论和实验方面深入研究的中心对象。特别是，了解这个希格斯玻色子是仅仅是标准模型（SM）希格斯玻色子，还是它是一个更普遍理论的一部分，是很有趣的。为了给出这个问题的答案，精确的理论预测是必要的，无论是在SM内还是在SM的扩展内。这些精确的理论预测将在本项目中讨论。环诱导过程在希格斯物理学中起着特殊的关键作用。由于希格斯玻色子只与大质量粒子配对，所以希格斯玻色子的产生和衰变过程涉及到初始或最终状态的无质量粒子，如胶子或光子，是通过一个大质量粒子环路进行的。这些环诱导的过程很重要，一方面因为它们对大型强子对撞机发现希格斯玻色子做出了重大贡献，另一方面它们对SM之外的新物理学很敏感。SM的希格斯扇区最简单的扩展之一是在SM场内容中添加一个额外的自旋零规单重态。该模型具有丰富的对撞机现象学，可以在大型强子对撞机上进行测试。这个模型还可以回答一些仍然悬而未决的问题，比如暗物质的本质问题，或者宇宙中物质-反物质不对称的起源问题。本项目将分析微扰理论中的电弱校正对环诱导过程的影响。由于循环诱导过程的首阶过程已经处于单环水平，次首阶修正的计算已经涉及到具有挑战性的双环图的计算。

One of the most important achievements of particle physics in the last decade was the discovery of a Higgs boson at the Large Hadron Collider(LHC) experiments. This new particle is now central object of intense investigations, both in theory and experiment, in order to precisely determine its properties. In particular, it is interesting to understand whether this Higgs boson is just the Standard Model(SM) Higgs boson or whether it is part of a more general theory. In order to give answers to this question precise theory predictions are necessary, both within the SM as well as within extensions of the SM. These precise theory predictions are addressed in this project.Loop-induced processes play a special key role in the context of Higgs physics. Since the Higgs boson only couples to massive particles, Higgs-boson production and decay processes which involve massless particles in the initial or final state, like gluons or photons, proceed via a massive particle loop. These loop-induced processes are important on the one hand since they contributed substantially to the discovery of a Higgs-boson at the LHC, on the other hand they are sensitive to new physics beyond the SM.One of the simplest extensions of the Higgs sector of the SM is the one with an extra spin-zero gauge singlet added to the SM fieldcontent. This model has a rich collider phenomenology which can be tested at the LHC. This model can also give answers to still open questions, which remain unanswered within the SM, like for example, the question of the nature of dark matter or the question of the origin of the matter-antimatter asymmetry of the Universe. Within this project the impact of electroweak correction in perturbation theory to loop-induced processes shall be analyzed. Since the leading-order process for loop-induced processes is already at the one-loop level, the computation of next-to-leading order corrections involves here already the computation of challenging two-loop diagrams.