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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 tt¯ 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
tt¯-associated production channel has the potential to discover this decay already at the HLLHC.
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.
