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Abstract

In this thesis we investigate theoretical frameworks for the characterization of dark matter and other new physics at colliders in combination with further experimental probes.To this end,we examine different theoretical approaches. Next-generation simplified models are the new benchmarks for LHC-based dark matter searches. We analyze and compare two commonly used instances of this class of models, namely a two-Higgs-doublet model extended with either a scalar or pseudoscalar mediator to the dark sector. We focus on the signatures in tt̄ resonance, mono-Z and mono-h searches. Those show an interesting interplay and distinguished signatures in the two models. Turning to more model-independent approaches, in addition to the dark matter searches, we investigate a new search channel for the rare Higgs decay to a Z boson and a photon, using effective field theory. This decay could still exhibit significant contributions from physics beyond the standard model. The proposed tt̄-associated production channel has the potential to discover this decay already at the HL-LHC. This would set strong constraints on so-far weakly tested modifications of the Higgs interactions. Back to dark matter, we examine the extended dark matter effective field theory. This framework allows the combination of various dark matter searches across different energy scales, in a model-independent and theoretically consistent quantum field theory, while providing a valid collider phenomenology. We perform parameter scans of increasing complexity taking all relevant constraints into account, and identify new viable parameter regions. Those non-trivial regions arise because of the more comprehensive framework, and are potentially testable in upcoming collider surveys. To further show the flexibility of this approach we apply slightly more specific versions to particular phenomenological interesting cases: di-fermion plus missing energy signatures at (future) colliders, and the excess in low-energy electron recoil events announced by the XENON1T collaboration