Searching for signatures of compositeness of the Higgs boson

Abstract: In this master thesis we consider some phenomenological aspects of two-Higgs-doublet models, both elementary and composite ones. The emphasis is on calculating and understanding first order phase transitions in such models, constrained to be in agreement with existing collider data on the Higgs sector. We also consider the contribution to the gravitational wave background of the universe that would originate from such phase transitions, in order to investigate whether the models could be probed through the LISA, BBO and DECIGO gravitational wave detectors that are being planned. As a proof of concept, we find that we can generate model realizations with such first order phase transitions in both elementary and composite models. In the elementary case, we find at least a few benchmark points that would be in the observable range of LISA. However, more data would be needed to properly investigate correlations between the gravitational wave signals and other aspects of the models, such as the collider phenomenology.