This thesis presents two phenomenological research projects focusing on the nature of Higgs bosons in quantum chromodynamics and tool building for precision studies of the Standard Model and beyond at the Large Hadron Collider.
The first project presents H1jet, a fast and easy-to-use program that computes the total cross-section and differential distribution in the transverse momentum of a colour singlet. In its current version, the program implements only leading-order 2 æ 1 and 2 æ 2 processes, but could be extended to higher orders. H1jet can be used by theorists to quickly assess deviations of selected new physics models from the Standard Model behaviour, and quickly obtain distributions of relevance for Standard Model phenomenology.
The second project presents a detailed study of Higgs interference effects at next-to-leading-order in the 1-Higgs-singlet extension of the Standard Model for the process pp (æ {h1, h2}) æ tt¯+ X. The interference effects have been studied for different benchmark points with heavy Higgs masses in the range 700–3000 GeV. For this purpose, gghtt, a parton-level NLO Monte Carlo event generator, has been developed, making it possible to study the interference effect between tree-level and loop-induced processes at NLO. Future versions of gghtt can easily be generalised
to work for any loop-induced process
