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This thesis describes two subjects from theoretical cosmology. The first concerns the creation of the matter--anti-matter asymmetry, which is generally assumed to be created in the early universe by a process called baryogenesis. The details of this process are yet unknown and there exist many models of baryogenesis in the literature. I study a specific model: "Cold Electroweak Baryogenesis". In particular I study the mechanism of the creation of particles in this model, and I estimate the size of the created asymmetry in this model. The result is that this specific model is unlikely to be able to produce a large enough asymmetry. The second subject deals with cosmological density fluctuations, which are observed in the Cosmic Microwave Background (CMB) radiation. According to the widely accepted inflationary paradigm, these density fluctuations are caused by quantum fluctuations during an early period in which the universe has expanded in an accelerated way. This period is called inflation and its underlying physics is still largely unclear. There is a plethora of models for inflation that predict characteristics of the fluctuations ("Quantum Cosmological Correlations") that are in agreement with the current observations. However it is possible that more precise future observations will enable us to differentiate between different models of inflation. It is therefore important to calculate the characteristics of the fluctuations to high precision. In general these calculations are very complicated, and one often uses the simplifying assumption that the evolution of the fluctuations in a certain regime can be described by classical physics. In this thesis I check this assumption by applying a classical approximation to the calculation in quantum field theory. The result is that this assumption is valid, although it is a little bit less good than was expected. |
