Dark Energy Perturbations And Integrated Sachs-Wolfe Effect

In1998, the type la supernova observations showed that the Universe has entered the epoch of the accelerated expansion. From then on, it has been one of the most important issues to explore the accelerated expansion of the Universe in the research of modern cosmol-ogy. In Einstein’s theory of gravity, it is implied that the present Universe is dominated by a mysterious component with negative pressure, called dark energy. In theory, various dark energy models are proposed by cosmologists. Not only does dark energy decide the present accelerated expansion and evolutive fate of Universe, but also dark energy perturbations play a crucial role in the observational constraints on models. The thesis is devoted to the investigation of some dark energy models about dark energy perturbations and integrated Sachs-Wolfe (ISW) effect.First of all, we introduce the research background of the thesis and present a brief re-view on the research contents and outline of the thesis. Then we start introducing the basics of cosmology, including the background cosmology and cosmological perturbations. Subse-quently, we give the brief introductions of some popular dark energy models and other two kinds of explanations for the accelerated expansion. The next section is the introduction of cosmological observations, which include the geometrical observations from expansion histo-ry and the dynamical observations from growth of structure. We begin our research work from Chapter4, where going beyond the background information, first we investigate the observational constraints on Ricci dark energy model with the inclusion of Ricci dark energy perturbations and discuss the evolutions of cosmological quantities and the features of CMB power spectra in this model. In addition, the holographic dark energy model with a new infrared cutoff is constrained by cosmological observations and the evolutions of cosmological quantities are investigated. In Chapter5, we calculate the ISW effect in the time varying vacuum model and Quintessence model with constant equation of state, respectively. The ISW effect arises from a time-dependent gravitational potential when dark energy dominates in the Universe at late time and leads to secondary cosmic microwave background tempera-ture fluctuations. Therefore, ISW effect provides a significant evidence for dark energy. We analyze the ISW-source term in two models. In Chapter6, basing on the inhomogeneous vacuum energy, we decompose the unified GCG model into interacting vacuum energy plus dark matter. We analyze the background evolution and linear perturbations for unified GCG and decomposed models. We illustrate the effects on CMB and matter power spectra. The decomposed models are constrained by different combinations of observational data. Finally, the summary and outlook are given in last chapter.