Next-to-simplified dark matter models

Laburpena

Dark matter constitutes the 27% of the energy content of the universe. However, the nature of dark matter is still a mystery. The Standard Model does not have any reasonable explanation to solve this problem, so the need for a theory beyond Standard Model is evident. In this context, simpli ed dark matter models are a good rst attempt to solve this problem. But simpli ed models are limited by their simplicity and in many cases experimental searches put several bounds on them, constraining severely the parameter space. For these reasons, a step forward is needed. One way to do that is to enlarge the particle content of this kind of models, looking for more realistic con gurations. In this thesis we adopt this idea of going next to simpli ed models and study two relevant models in the context of dark matter portals. In the rst one we re-visit the well known singlet-scalar Higgs portal, one of the simplest dark matter models, consisting of a singlet-scalar coupled to the Higgs boson. This model is of great interest since, with just an extra particle, it can reproduce the dark matter density and has a rich phenomenology. However, since its postulation, experimental searches have tested the model putting severe bounds on its parameter space and nowadays is close to be excluded. A simple way to relax these constraints is to extend the dark sector. In this thesis we study the case of the simplest extension, adding an extra singlet-scalar. We analyze the new phenomenology due to this new scalar, specially coannihilation e ects. Also, we impose the experimental constraints in the extended model to see how the new parameter space is restricted. Finally, we test how well this model can explain the galactic center excess. On the other hand, we study another kind of dark matter portal, called Z0 portal. This scenario implies the existence of an extra U(1) symmetry in the gauge group. In this kind of framework the strongest constraints come from di-lepton searches at colliders and bounds from direct detection experiments. A simple way to relax these constraints is to choose a leptophobic mediator, i.e. with no direct couplings to leptons, and interacting axially to the dark matter particle, so that the coupling between the dark matter and quarks is spin-dependent. Taking this considerations into account, we look for the simplest possible con guration that ful ll these requirements and cancels the anomalies of the new gauge group, and we study the phenomenology of a representative model of this kind.