Cosmological perturbations in string gas cosmology
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Date
2011.
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Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2011.
Abstract
The current model of the early universe is mainly based on the in ationary scenario. Despite its phenomenological success in providing a solid mechanism for the generation of cosmological uctuations in the early universe, this scenario su ers from several conceptual problems. Therefore, it is important to investigate the subject within a fundamental theory. Driven by this motivation, in this thesis, we study the cosmological perturbations in the string gas cosmology formalism. First, we give a review on string thermodynamics. Then we go over a recently proposed scenario of producing scale-invariant cosmological perturbations and examine its problems. Finally, we discuss an alternative model based on the open strings attached on a D-brane and nd out that it is hard to realize a scale-free spectrum for the cosmological perturbations.