Searching for a resolution of BSM puzzles at accelerators and in space

Abstract

Particle physics is right now in a unique situation: the most successful description of fundamental interactions that we have, the Standard Model, is evidently incomplete, lacking the explanations of dark matter, neutrino masses, and matter-antimatter asymmetry in the Universe. Yet, none of experimental tests show any reliable disagreement with model's predictions. At the same time, the number of proposed solutions to these Beyond the Standard Model problems grows steadily. It is important to analyze the whole landscape of existing data with an emphasis on two most important questions: what models offer the best balance between minimality and explanatory power, and what experiments can cover the gaps in our exploration of new physics at minimal cost? The thesis is dedicated to these questions, with a focus on the most prominent candidates for the answers: the model of Heavy Neutral Leptons and the SHiP experiment that aims to search for light feebly interacting particles.