Phenomenological Studies in Cosmoparticle Physics : Expansion Histories in non-Einstein Gravity and Dark Matter at the Large Hadron Collider

Abstract: As the Big Bang model has become established, the fields of cosmology and particle physics have become intertwined. A range of observations forces us to consider the phenomena of dark matter and dark energy. This interpretation is based on our understanding of gravity, while the standard model of particle physics describes the other fundamental forces in nature and fails to explain the dark components. This thesis includes two different types of studies where hypotheses of physics beyond the standard models of particle physics and cosmology are faced with what observations and experiments can tell us.The first one deals with the possibility that our theory of gravity is what has to be modified at large distances to explain the dark energy, which then need not be a contribution to the energy content at all. The expansion histories in two such frameworks are tested with data from type Ia supernovae and measurements of the baryon acoustic peak in the galaxy distribution as well as in the cosmic microwave background.The second type of study concerns the possibility of establishing the particle nature of dark matter through interactions other than gravitational. While there are ways of doing this using astrophysical observations, the uncertainties due to astrophysics and the unknown distribution of the dark matter are large. High energy particle colliders provide a way of imitating the conditions of the early universe in the laboratory, where we can hope to produce yet unknown heavy particle states and in a more controlled environment determine their properties. We study the prospects for discovering two types of weakly interacting dark matter candidates at the CERN Large Hadron Collider.