Investigations On Thermal Non-Gaussianity And The NAQDE Dark Energy Model

Cosmology is experiencing a precise epoch since the last decade of twentieth century.The origin and the evolution of large scale structure and dark energy are two hot issues of modern cosmology.This thesis mainly focus on the thermal non-Gaussianity and NADE dark energy model.In this thesis,firstly,the background of cosmology and the standard cosmological model are reviewed.Then we give brief review on non-Gaussianity and thermal fluctuationsSecondly,we investigate the thermal non-Gaussianity in holographic cosmology, semiclassical loop cosmology and Near-Milne universe.In holographic cosmology, semiclassical loop cosmology and Nera-Milne universe,due to introducing new physics,a purely thermal fluctuations give rise to an almost scale invariant spectrum of metric perturbations.Here we calculate the thermal non-Gaussianity.We find that, in holographic cosmology,if the matter is phantom-like,the non-Gaussianity f_NL^equil can reach O(1) or even be larger than O(1).Especially in the limitω→-5/3,the non-Gaussianity is very large and negative.Furthermore,since the energy is proportional to the area,the thermal holographic non-Gaussianity depends linearly onκif we neglect the variation in T during the transition.We also investigate the non-Gaussianity in semiclassical loop cosmology and Near-Milne universe.We find that in semiclassical loop cosmology,the non-Gaussianity is suppressed.In Near-Milne universe,if consider the no phase transition case,the non-Gaussianity is proportional toκ^-3γ,γ＞0.It is very different from the other cases such as the thermal fluctuations in holographic phase and string gas cosmology.Thirdly,we review the some dark energy models,then implement the new agegraphic dark energy model with quintessence field.We demonstrate that the new agegraphic evolution of the universe can be described completely by a single quintessence fiele.Its potential as a function of the quintessence field is reconstructed numerically.In particular,the analytical solution of the new agegraphic quintessence dark energy model(NAQDE) is approximately obtained in the matter-dominated epoch.Furthemore,we investigate the evolution of the NAQDE model in theω-ω′phase plane.It turns out that by quantum corrections,the trajectory of this model lies outside the thawing and freezing regions at early times.But at late times,it enters the freezing regions and gradually approaches to a static cosmological constant state in the future.Therefore the NAQDE shoule belong to the freezing model at late times. For comparison,we further extend this model by including the interaction between the NADE and DM and discuss it evolution in theω-ω′phase plane.