UC Santa Barbara

In this thesis, we study some possible extensions of the Standard Model and the insight they provide into treating the Standard Model as an effective field theory. Following an introduction highlighting the uses and difficulties of effective field theory in study of the Standard Model and physics beyond the Standard Model (BSM), we first focus on Loryons, particles which acquire most of their mass from the Higgs. We explain how BSM Loryons necessitate the use of HEFT as an effective field theory description and examine the experimental viability of scalars and vector-like fermions. We then investigate how BSM Loryons could affect the electroweak phase transition and gravitational wave background. Finally, we analyze the effective field theory of the two Higgs doublet model, demonstrating the importance of choosing an appropriate flavor basis for the two doublets and introducing a new basis particularly suited to effective field theory analysis.