Signatures of Dark Matter at the LHC : A phenomenological study combining collider and cosmological bounds to constrain a vector dark matter particle model

Sammanfattning: Everything that humans have ever touched, created or built something from consists of a type of matter that only makes up 15 percent of the total matter in the universe. The remaining 85 percent is attributed to dark matter, a so far not discovered and non-luminous type of matter. In this thesis a potential dark matter particle candidate has been studied by investigating an extension of the SU(2) symmetry into a dark gauge sector, where the new sector is connected to the standard model through a vector-like fermion portal. In order to understand how such an extension is made, the Lagrangian density of the standard model and its different gauge sectors were derived. The cross sections of the process of pair production of dark matter particles and tau leptons in the final state due to proton-proton collisions at the LHC was simulated with the software \texttt{MadGraph}. The cross sections were used to draw significance contours for the exclusion and discovery regions for parts of the parameter space of the new model, for current and projected luminosities of the LHC. The projected luminosity scans also consider how lowering the uncertainty in the number of background events through hypothetical improvements to detectors would impact the exclusion and discovery contours. The significance contours were combined with relic density constraints, derived from comparisons between measurements of the Planck telescope and calculations from the software \texttt{MicrOMEGAs}. The resulting graphs show that there are non-forbidden regions of the parameter space that are significant for exclusion and discovery for luminosity of current searches. Increasing the luminosity while keeping the uncertainty in the number of background events the same yielded only minor increases to the exclusion and discovery contours. Combining the projected luminosities with improvements to the background uncertainty instead produced exclusion and discovery regions that were significantly larger than those for the current luminosity.