A Global Fit Study On Holographic Dark Energy Models

In history, the discovery of the expansion of our universe fundamentally changed peo-ple’s knowledge of the universe that she is static and eternal, which directly prompted the establishment of the "Big Bang" theory. Coincidentally, in recent years the discovery of acceleration of present universe’s expansion also make people have a new understanding on the features of matter, which aroused a heated discussing on the dark energy. The development of the observation provides a good opportunity for studying dark energy and other cosmological issues. Currently, using the combination of many independent observations to constrain the cosmology parameters has become a standard approach. Especially, performing a global fit study on the dark energy models using the full obser-vational information of the Cosmic Microwave Background (CMB) gets more and more attentions. In this thesis, our main work is doing such an analysis on the holographic dark energy (HDE) and the new agegraphic dark energy (NADE) models. For the global fit study on the HDE model, we consider the influence of spatial curvature and mas-sive neutrinos on the evolution of HDE, and calculate the perturbation of HDE with the parameterized post-Friedmann method which can correctly deal with the perturbation’s divergence when w crossing-1. We found that it could greatly reduce the confidence level of c<1when we considered the spatial curvature, implying that the inclusion of spatial curvature in the HDE model might be helpful to alleviate the future doomsday problem. Besides, we first obtained the result of the sum of neutrino mass in the HDE model. We also studied the effects of the phenomenological parameter c on the back-ground evolution, matter perturbation’s evolution, CMB power spectrum, and structure growth. We found that when c-0.7HDE model could produce a nearly indistinguish-able results with the ACDM model. For the NADE model, we first performed a global fit analysis on it. We discussed the initial problem of the NADE model and gave a new initial condition available in a universe with radiation and spatial curvature considered as well. The fitting results showed that with the new initial condition the NADE model could be constrained tightly and it preferred an open universe with a negativeo-Moreover, the obtained best-fit value of parameter n in the NADE model was significantly smaller than those obtained in previous works. Our further test indicated that such a change resulted from the different supernova samples used, and the new constraint results of the NADE model obtained in this work were more reasonable than before.