Evolution Of The Universe Under The Influence Of The Modfied Holographic Ricci Dark Energy

With the development of astronomical observation technologies, more and more observation data provide that the expansion rate of our universe does not slowdown under the influence of the gravitational force, but be quickened in pace under the influence of a mysterious force. The mysterious force is known as "dark energy". On the other hand, the holographic principle is considered as one of the foundations of quantum gravity, then, the nature of dark energy is certain to be associated with the holographic principle. The holographic dark energy models provide a more simple and reasonable frame to investigate the problem of dark energy, and these models are helpful in solving the fine tuning problem and the coincidence problem. Therefore, it is very significant to study the holographic dark energy’s character and its influence on the universe’s evolution.In this paper, by analysing the state parameter, the energy density and the statefinder parameter, the evolution of the modified holographic dark energy is studied. Meanwhile, in the universe filled with dark energy and dark matter, the motion equation of the test particles in the local gravitational bound system, the holographic Ricci dark energy interacting with dark matter in the nonflat universe and the generalized second law of thermodynamics on different horizons in the anisotropic universe are studied. The main results obtained in this paper also have been given as below:1. In the local gravitational bound system corresponding to the Milky Way galaxy, using an interpolating metric, which is a static Schwarzschild metric in the small scale and a time-dependent Friedmann spacetime in the large scale, the test particles’ function of effective potential and radial equation of motion are given. The results show that the galaxy would go through three stages:expands from a singular point; stays in a discoid for a period of time; big rip. With the help of analysing the critical angular momentum, it is easy to find that the test particles need less angular momentum to escape from the center mass as time passes.2. Considering the apparent difficulties of cold dark matter in reproducing some observations related to the matter power spectrum on small scale structure, we have studied the modified holographic Ricci dark energy coupled to interacting relativistic and non-relativistic dark matter in the nonflat Friedmann-Robertson-Walker universe. We find that the transition time of the universe from decelerating to accelerating phase in our model is close to that in the ACDM (Lambda Cold Dark Matter) model, and the dark energy holds the dominant position from the near past to the future. By studying the statefinder diagnostic and the evolution of the total pressure, one can find that this model could explain the universe’s transition from the radiation to accelerating expansion stage through the dust stage. According to the Om diagnostic, it can be easily found that when the interaction is weak and the proportion of relativistic dark matter in total dark matter is small, this model is phantom-like. In general, the interaction and the relativistic dark matter’s proportion all have great influence on the evolution of the universe.3. The evolution of the anisotropic Bianchi type Ⅰ universe is studied, and one can find that the modified holographic Ricci dark energy is matter-like in the early time of the universe, but phantom-like in the future. The evolution of the deviations of state parameter and the total pressure of the universe shows that for an anisotropic Bianchi type Ⅰ universe, it can transit from a high anisotropy stage to a more homogeneous stage in the near past. Using the normal entropy given by Gibbs’ law of thermodynamics, it is proved that the generalized second law of thermodynamics is valid when the universe is enclosed by the apparent horizon. However, if the infrared cutoff radius L is taken as the horizon, the generalized second law of thermodynamics is not always satisfied throughout the history of the universe. It is invalid in the near past to the future, which is helpful in explaining the formation of the galaxies.