Some Issues In Dark Energy Cosmology

With the discovery of the present cosmic acceleration in the end of last century,dark energy and cosmological constant problems have been one of the most important issues in the research of contemporary physics and cosmology.In this thesis,beginning with the discussion on the cosmological dynamics and the cosmic acceleration,the cosmological constant and its problems are presented.Then,several dynamical dark energy models are reviewed in Chapter 2.The holographic dark energy is a typical example to probe the nature of dark energy, within the fundamental theory framework.In this model,the fundamental principle of quantum gravity,the holographic principle,is considered.Generalizing the original holographic dark energy,the evolutions of the holographic dark energy in a non-flat universe as well as in a cyclic universe are studied.Besides,in Chapter 3,there is an interacting holographic dark energy model constructed,for the interaction between dark energy and dark matter is often considered to alleviate the coincidence problem;the effect of interaction to the cosmological evolution is also investigated for this interacting holographic dark energy model in this chapter. In addition,recently,the agegraphic dark energy models were proposed,by considering the famous uncertainty relation in quantum mechanics together with the gravitational effect in general relativity.In this regard,the holographic and agegraphic dark energy models may posses some significant features of an underlying theory of dark energy.On the other hand, with the accumulation of the current observational data as well as the rapid developments of the technology for space probe,the cosmological research has entered the epoch of the precise cosmology.Thus,nowadays,all dark energy models have to face the test of cosmological observations.A typical approach for this is to predict the cosmological evolution behavior of the models theoretically,and to make a consistency check of models by comparing it with observations.An alternative approach is to start from observational data and to reconstruct corresponding theoretical Lagrangian.It seems that the latter is more efficient to find out the best-fit models of dark energy from observations.Reconstruction procedures according to observational data have been called forth with great enthusiasm in cosmology:In Chapter 4, the scalar field models of holographic dark energy and agegraphic dark energy are discussed, based on the best-fit results of the observational data.Also,the generalized ghost condensate model of dark energy is reconstructed in this chapter.Finally,in Chapter 5,the statefinder diagnostic is used to discuss several dark energy models.