Robert Mardoff Nielsen: Spherical Collapse in Dark Energy Models
This thesis is a study of the dynamics and virialization of cosmic structures in the framework of flat cosmological models where the properties of the dark energy component plays an important role in the global and local dynamics of the Universe. In particular, the analysis focuses on the study of the spherical collapse model which represents a spherical homogeneous density perturbation in the cosmic fluid. It is a two-component system, made of cold dark matter and dark energy, which initially evolves with the Universe and with time begins to decouple from the background expansion and starts to "turn around'' and finally collapse. It is taken into account many models with an equation of state which are constant in time. Three main conditions for virialization will be considered and compared, and some differences in characteristic parameters will be pointed out, such as the radius and density contrast when the structures have virialized to a final size.