The Study Of Dark Energy And Its Thermodynamical Properties

It has been confirmed that the expansion of our universe is accelerating at present, through numerous cosmological observations, such as the type Ⅰa Supernova, the cosmic microwave background anisotropy, the Sloan Digital Sky Survey and the large scale structure. Therefore, it has been one of the most important issues in the research of cosmology to explain the accelerating universe. Up to now, the popular explanation is that the present universe is dominated by an exotic component, dubbed dark energy, which is introduced to explain the accelerating expansion through negative pressure. In addition, modified gravity theories (f(R)) and higher-dimensional theories are also studied to interpret the accelerating universe.A brief introduction of the background knowledge of cosmology are given at first (chapter1), which including the cosmological Principle, the standard cosmological model and the inflation cosmological model. Then we introduce some famous dark energy model and make some brief summary of their evolutions. Our work include in the chapters from3to5. Firstly we emphasized the evolution of Variable Modified Chaplygin Gas Model and the Variable Modified Chaplygin Gas Model with Interaction (chapter3). Specifically, the evolutions of related cosmological parameters such as the state parameter of dark energy wde, the fractional energy densities Ωi (i respectively denotes baryons, dark matter, dark energy), the deceleration parameter q. As the combination of the growth index f and the function H(z) can provide significant insight into the properties of dark energy and interpret the structure formation. We also discuss the growth index f in the VMCG model. Furthermore, the statefinder diagnostic is used to discuss the Variable Modified Chaplygin Gas Model with Interaction.On the other hand, when local thermodynamic equilibrium, universe can be considered as a thermodynamical system. In a general independent dark energy model ω=ω0+ω1z(1+z)/(1+z2), we investigate the thermodynamical properties on the apparent horizon and event horizon (chapter5). In Chapter4, by adopting Markov Chain Monte Carlo method, Variable Modified Chaplygin Gas Model is constrained on the basis of the current observed data (SNIa, CMB, BAO, OHD). By using the mean values of parameters, we also studied the thermodynamical properties of the Variable Modified Chaplygin Gas Model (Chapter5) on the apparent horizon, event horizon and particle horizon respectively.A conclusion is presented in the last section.