Abstract

This thesis investigates Beyond Standard Model (BSM) physics, focusing on three interconnected studies addressing fundamental puzzles in the Standard Model (SM) of particle physics. First, we examine the supersymmetric U(1)R × U(1)B−L model with both universal and non-universal boundary conditions at the GUT scale, studying its implications for dark matter, the muon g − 2 anomaly, and collider signals. Detailed reconstruction of final-state leptons establishes benchmarks with significance levels exceeding 5σ at the High-Luminosity LHC (HL-LHC). Second, we explore vectorlike leptons (VLLs) as extensions to the SM, demonstrating their potential to resolve both electron and muon anomalous magnetic moment discrepancies while consistent with the neutrino data. Six-lepton signatures can be clearly distinguished from SM
backgrounds at future hadron colliders operating at 100 TeV. Finally, we establish improved sensitivity to type-I seesaw superheavy Majorana neutrinos at future muon colliders in vector boson fusion (VBF). We show that μ+μ− colliders at 10 TeV and 10 ab^−1 integrated luminosity can exclude heavy Majorana neutrinos with mixing parameters |VμN| down to 10^−3 for masses up to 100 TeV. Altogether, these three studies target major sectors of BSM phenomenology through detailed present and future collider projections, providing compelling motivation for future experiments.