The Theoretical And Numerical Research Of Holographic Dark Energy Model

Dark energy is one of the most challenging problems in modern cosmology and physics. In order to understand the nature of dark energy, numerious theories and models have been proposed and constructed. Among them, the holographic dark energy (HDE) model, proposed by my advisor Prof. Miao Li, has attracted lots of attention. This thesis provides a brief introduction of our theoretical and numerical investigations on the HDE model.Since its proposal, HDE has gained great success in both theoretical and observational aspects. However, there are still some problems not extensively studied in this model. One of the most attracting problem is the problem of cosmic doomsday——based on current cosmological observations, HDE predicts a big rip fate of the universe. To solve this problem, we considered some tentative generalizations of the original HDE model.One of our trial is the consideration of the possible interaction between HDE and dark matter (i.e., the "dark sectors"). Phenomenological, we considered the Q∞ρdmαρdeβ forms of interaction terms. Compared with the commonly studied Q∞Hρdm,Q∞Hρde forms of interaction, our consideration is not only universal but also physically plausible. Based on the latest cosmological observations, we performed detailed investigations on the strength and forms of the interaction. We found that, in the2σ confidence level (CL), the observational constraint on the increment (decrement) of dark matter is less than9%(15%)。We also found that, in case of a large enough β, the dynamical equations of dark sectors have a approximate de Sitter solution in the future, which helps us to evade big rip. The reason is that the powerful interaction in the future prevent the dark en-ergy density from infinitely increasing. We further investigate the observational constraints on the parameter space, and found that such stable solutions can be achieved in2σ CL.To further investigate the physical interpretations of the HDE model, we proposed a generalized holographic dark energy (GHDE) model by considering the parameter c of the original HDE model as a time-dependent function c(z). By choosing four four kinds of parametrizations of c(z), we reconstructed the evolution of dark energy from the joint analysis of the present observational data. We found that, compared with the original HDE model, the GHDE models can provide a better fit to the data. We also found that, unlike the original HDE model with a phantom-like behavior in the future, the GHDE models can help us to evade the big rip fate of universe. Our investigation shows that the generalization of c have abundant cosmological interpretations.