Phenomenology in multi-scalar extensions of the Standard Model

Summary, in English

This thesis is composed of four papers, which all treat various extensions to the Standard Model (SM). The first two papers concern a particular supersymmetric, grand-unified theory (GUT), while in the latter two, we classify anomaly-free implementations of two-Higgs doublet models (2HDM) with a gauged abelian symmetry.

Paper I. In this paper, we present an alternative solution for avoiding GUT-scale lepton masses in so-called trinification based GUT-models (T-GUTs). Rather than introducing several copies of the tri-triplets, which is the conventional approach, we solve the issue by embedding the symmetries into an E8 group.

Paper II. This paper involves a more detailed study of the model proposed in Paper I. Some of its features is an absence of the mu-problem and a universal Yukawa coupling for all chiral fermions.

Paper III. Here, we classify all anomaly-free implementations of a 2HDM with a gauged Abelian symmetry and the SM fermion content. The resulting 11 models are then compared under a range of experimental bounds, from which we identify the most promising ones.

Paper IV. In this paper, we again classify and compare all anomaly-free implementations of a 2HDM with a gauged Abelian symmetry, but this time around also including two generations of right-handed neutrinos. The right-handed neutrinos are incorporated to provide a mechanism for the neutrinos to obtain a mass, here via a type-I seesaw mechanism. In total, there are 16 valid models, which are all compared, both for normal- and inverted ordering. Two models are identified as the most promising candidates for future studies.