Precision Calculations for Dark Matter Searches in Supersymmetry and in Simplified Models

Abstract

The study of physics beyond the Standard Model is one of the main focuses of particle physics, in which many questions remain unanswered and none of the proposed solutions has emerged as the most probable. Confirming or disproving whether a model is realised in nature requires a precise study of its phenomenology. In quantum field theory, such calculations are often performed using perturbative techniques. The high degree of precision necessary to assess the correctness of the predictions of a given model means, in this context, taking into account higher-order corrections in the interaction in consideration. In this thesis, we calculate next-to-leading order corrections in the strong coupling (or NLO-QCD corrections, from quantum chromodynamics) for several processes in the context of supersymmetry and dark matter searches. We calculate NLO-QCD corrections to the weakino-squark production processes in the Minimal Supersymmetrical Standard Model (MSSM), including the subtraction of the on-shell resonances appearing in the real emission corrections to this process. We match the fixed-order calculation to the parton-shower (PS) program PYTHIA using the POWHEG method. We can therefore calculate the NLO-QCD cross sections including PS effects for these processes and generate differential distributions at the NLO+PS level. These processes are responsible for interesting experimental signatures, like hard jets and large quantities of missing transverse momentum. Our code will be publicly available for future phenomenological and experimental studies. Additionally, we study the phenomenology of dark matter pair-production processes at hadron colliders in the context of simplified models, studying the similarity between these processes and the production of neutralino-pairs in the MSSM. We perform this comparison at NLO-QCD accuracy, exploring a vaste range of supersymmetric scenarios. Simplified models are often interpreted as low-energy limits of a UV-complete theory, and we aim at understanding to what extent an s- and a t-channel model are able to reproduce the phenomenology of the far more complex MSSM. We also investigate the same simplified models for dark matter in a completely different scenario, namely direct detection experiments. We calculate NLO-QCD corrections in the non-relativistic regime and match our results to the Wilson coefficients and operators of an effective field theory, to express our results in the terms generally used for experimental results in direct dark matter searches. We then perform a phenomenological study, comparing the limits set in collider searches and the ones set by the direct detection experiments CRESST and XENON.