PHENOMENOLOGY OF THE STANDARD MODEL AND BEYOND

Abstract

While the Standard Model (SM) of particle physics is the most precise theory everdiscovered, it is known to be incomplete. The SM cannot account for the observed Dark Matter (DM) in the universe or that the neutrinos have masses. Furthermore, theoretical puzzles such as the matter-antimatter asymmetry and the Planck-weak hierarchy remain unexplained within the SM. These shortcomings have motivated extensive efforts to search for physics beyond the SM (BSM). One promising class of BSM theories involves “Hidden Sectors”, which are newparticles and interactions that are singlets under SM gauge symmetries. While minimal hidden sector scenarios have been widely studied, models with non-minimal field content and richer dynamics remain less explored. In the first part of this dissertation, we examine both minimal and non-minimal hidden sector models, addressing open questions regarding their discovery potential. We evaluate the sensitivity of future lepton colliders to vector portal models across a range of benchmark scenarios, and demonstrate how neutrino telescopes can probe non-minimal hidden sectors using two simplified models. Precision measurements of SM observables, such as electroweak precision observables (EWPOs) and the anomalous magnetic moment of the muon (g − 2), offer a complementary approach to direct searches by probing virtual effects of new physics. A crucial input to global EW fits is the top quark mass mt, which must be knownwith high precision to fully exploit the sensitivity of these observables. However, most current methods are limited by uncertainties in production modeling (including possible BSM effects therein) and jet energy calibration. In the second part of this dissertation, we propose a new method for measuring mt that reduces these sources of systematic uncertainty while involving complementary systematics. If implemented, this approach could significantly enhance the precision of current and future measurements, helping to sharpen indirect probes of BSM physics.