Advances in Precision Calculations of Higgs Boson and Single Top Quark Production at the Large Hadron Collider

Since the discovery of the Higgs boson in 2012, particle physics has entered an era of precision. With the upcoming increase in luminosity of the Large Hadron Collider (LHC), we will gain access to deep and detailed insights into the behaviour of fundamental particles. On the theoretical side, the description of partonic cross sections with next-to-next-to-leading order (NNLO) accuracy in Quantum Chromodynamics (QCD) is becoming a standard.

Despite the astonishing agreement between the experiments and theoretical predictions, it is clear that the Standard Model (SM) of particle physics is incomplete. One way to search for New Physics is to push the accuracy of the theoretical predictions and experimental measurements further. In this thesis, we study three problems related to precision description of Higgs boson and top quark production at the LHC.

In the first part, we investigate the interference contribution between two Higgs production mechanisms in the pp → H + jetc process. This process can be used to study the Yukawa coupling of the charm quark. The interference studied in this thesis requires a helicity flip on the charm-quark line, forcing us to treat the charm quarks as massive. ... mehrThis requirement leads to unconventional QCD phenomena, such as the importance of soft quarks and unusual collinear factorisation.

In the second part, we calculate the so-called non-factorisable corrections to t-channel single top production. These corrections arise from the crosstalk between the two fermion lines present in this process. Until now, the non-factorisable contributions to single top production have been neglected because they do not appear at next-to-leading order (NLO) and they are colour-suppressed compared to the factorisable ones. However, recent studies indicate that the factorisable corrections are relatively small at NNLO and that the non-factorisable ones can be dynamically enhanced. We compute the non-factorisable corrections and discuss their numerical impact on t-channel single top production at the LHC and the Future Circular Collider (FCC).

In the third part, we consider the same type of corrections to Higgs production in weak boson fusion (WBF). Contrary to the case of t-channel single top production, an exact computation of these corrections is currently impossible. We construct an expansion of the double-virtual contribution around the forward limit of the tagging jets. It turns out that the expression of the double-virtual contribution at the next-to-leading order in the eikonal approximation can be expressed in a quite compact form.