Specification Gravitational Cosmology

In the late1990s, astronomers discovered the cosmic accelerationvia the observations of type Ia Supernovae, which conflicts with ourbasic understanding of gravity. To explain this weird phenomenon,theorists proposed various models. In this dissertation, we investigatecosmological models based on two gauge theories of gravity, andexplain the cosmic acceleration in these two frameworks. In the firstpart, we introduce the history of gauge theory and the basic thoughtsabout gauge theory of gravity, especially the Poincar′e gauge theory,and present the field equation of gravity.In the second part, the cosmological implication of Poincar′egauge theory is explored, especially the model only with the torsionrelated to0+mode. We obtain the exact solutions of the evolutionequation with constant curvature, which unfortunately are notphysically acceptable. For this reason, we are forced to investigate thenon-constant curvature case, in which we obtain the analytical solutionof the past-time evolution and approximate solution of the very latetime evolution. Next, we compare these theoretical results with the TypeIa Supernovae observation data, and obtain the best-fit value formodel parameters and initial conditions, and also the confidence levelof these parameters. At last, the evolution equations are solvednumerically by means of these constraints of parameters, and theresults are consistentwith the former analytical discussion.In the last part, we research the cosmology based on anothergauge theory of gravity-de Sitter gauge theory. We rewrite theevolution equation as a set of dynamical equations, which comprise acomplete autonomous system, and conduct the dynamics analysisabout this system. We find9critical points, also their stabilities. Next we compare this model with Type Ia Supernova observationdata, and obtain the best-fit value of these model parameters andinitial conditions, and also the confidence level of them. In the end, wesolve the evolution equation numerically using the constraints ofparameters, and the results are in accord with the former qualitativediscussion.