Dark matter and dark energy are among the top unsolved mysteries within today’s physics and astronomy. These unknown phenomena are each supposed to explain a set of otherwise very puzzling...Show moreDark matter and dark energy are among the top unsolved mysteries within today’s physics and astronomy. These unknown phenomena are each supposed to explain a set of otherwise very puzzling observations. However, instead of introducing two unknown new forms of matter, one could equally try to unify their concepts into one. This is exactly what Unified Dark Matter models try to do. For this approach to work such models need to behave as dark matter on relatively small scales (to account for structure formation), and as dark energy on relatively large scales (to account for accelerated expansion). In this thesis the simplest unified dark matter model is considered: the Chaplygin gas. In particular, we investigate the possiblity for dark matter halo-like objects within this model. We set up a general framework and try to solve the relevant equations for both small radii and large radii close to the de-Sitter radius. The solutions constructed indeed show large concentrations of energy density are allowed, and in some cases the two regimes can be reasonably matched.Show less
Symmetry breaking in realistic supersymmetric theories has proven to be difficult without the introduction of explicit supersymmetry breaking terms. In this thesis we investigate symmetry breaking...Show moreSymmetry breaking in realistic supersymmetric theories has proven to be difficult without the introduction of explicit supersymmetry breaking terms. In this thesis we investigate symmetry breaking through the Fayet-Iliopoulos mechanism in a U(1) extended non-minimal supersymmetric standard model incorporating massive right-handed neutrinos and a new scalar field. We derive the potential of the theory and show the Fayet-Iliopoulos mechanism alone does not suffice to obtain realistic symmetry breaking. We conclude that explicit supersymmetry breaking terms are required to obtain realistic symmetry breaking in this model.Show less
