Some Topics On Dark Energy

In recent years, numerous measurements all suggest that the universe is currently accelerating and is dominated by a component with negative pressure, which is named as dark energy. It permeates homogenously in all the universe and pushes the accelerated expansion of the universe. Although dark energy has been preliminarily known, its nature still remains mysterious. Dark energy has become one of the most important problems in the research frontier of physics and cosmology.In this thesis, after briefly reviewing the background of cosmology and the standard cosmological model, we present some fashionable dark energy models.After that, we investigate cosmological dynamics of scalar fields in the presence of a barotropic perfect fluid. The dynamical dark energy models driven by a scalar field suffer from the so called fine-tuning problem and coincidence problem, In order to address these problems, one may employ scalar field models exhibiting scaling solutions. Here we first explain the property of an autonomous system before entering the detailed analysis. Then we present the associated equations of motion for the tachyon field including the background fluid in spatially curved FRW universe and obtain the scaling solutions. Furthermore, by investigating the nature of scaling solutions, we determine whether such behavior is stable or just a transient feature. Then we turn to construct the scalar potential leading to such scaling solutions. In particular, its asymptotical forms are obtained in various circumstances for spatially open and closed universe respectively.In chapter four, we are interested in the impact of dark energy on the perihelion shift of planets. For Mercury, we find an additional contribution due to dark energy, which is approximately 1/10000 of the total angular of the perihelion shift. Thus, it is possible to determine the equation of state of dark energy by observing the perihelion shift of Mercury. Furthermore, the conclusion may be helpful for checking up the dark energy models.Chapter Fiver is both a conclusion and a prospect. It sums up the entire dissertation, and looks into the future work.