Beyond the Standard Model Higgses at Future Colliders

Motivated by several long-standing puzzles confronting the Standard Model (SM) in particle physics, many Beyond Standard Models (BSM) with extended Higgs sectors were proposed. The Two-Higgs-Doublet Model (2HDM) is a prototype model with two doublets in the Higgs sector. Other than the SM-like Higgs h, the low energy spectrum of 2HDM contains four BSM Higgs states, the neutral CP-even Higgs H, the neutral CP-odd Higgs A and a pair of charged Higgs H±. Along with the four incarnations, namely type-I, type-II, type-L and type-F, it provides rich phenomenologies for exploration. In this thesis, we explore four types of 2HDMs at several future colliders as well as the opportunities to distinguish them. Two general methods are employed: the direct search at a future 100 TeV pp collider and a multi-TeV muon collider and the indirect search at several proposed Higgs factories and Z-factories. With direct search, we study the exotic charged Higgs decay H± -> HW± in a hierarchical Type-II 2HDM at a 100 TeV pp collider and find that almost the entire space can be probed after combining with other exotic Higgs decay modes. In addition, due to the clean environment at a muon collider, it allows the probe of heavy BSM Higgses at an unprecedentedly high scale and offers remarkable chances for discrimination among the four types. With an indirect search, BSM Higgses are explored by accurately studying their corrections to the SM Higgs and Z-pole precision observables. For illustration, we study the impact on Type-I 2HDM and find the parameter space can be tightly constrained. The discovery potential and the extent to which the four types of 2HDMs could be distinguishable are also examined. We find that most of the currently allowed parameter regions permit a 5σ discovery at future Higgs factories and the four types of 2HDMs can be largely distinguishable once a 5σ discovery is made