Studies of fermion masses in Gauge theories

Abstract: The Electroweak Standard Model of particle physics has proved to be avery successful theory. Nevertheless several questions have been raised dueto shortcomings of the model. The most outstanding question in this modelconcerns the origin of masses of the elementary particles. Eventually wehope that a more fundamental theory will explain the masses. In order toget some clues as to how this more fundamental theory may be, we studysome models in which one can derive the masses. In this thesis four suchstudies are presented and their implications are discussed.From the motion of stars and galaxies one deduces that probably notall the mass in the Universe is luminous and that there is need for ”DarkMatter”. Presently we do not know whether this ”Dark Matter” consistsof the kind of matter we already know or if it has to be some new kindof matter. It may well be that this matter contributes substantially tothe mass of the Universe. In this thesis a study is presented concerningthe different scattering processes involving one of the most popular ”DarkMatter” candidates.