Theoretical Studies On The Reduced Modified Chaplygin Gas Cosmology

To explain the accelerating expansion of our universe,people often consider two solutions:modifying the gravity theory of general relativity or constructing the dark energy models,such as the high-dimension gravitational models inspired by the extra-dimension theory,the modified Chaplygin gas?MCG?model,the cosmological constant model,and so on.Dvali-Gabadadze-Porrati?abbreviated as DGP?brane-world model is one of the modified gravitational model,where our universe is considered as a 4-dimensional brane embedded in a 5-dimensional flat spacetime.Though the self-accelerating branch in DGP model can achieve accelerating expansion of the late universe without introducing any extra components,there are several unsatisfactory problems in this model.In the normal branch of DGP model,it is necessary to introduce extra dark-energy components to drive the cosmic acceleration.In the second chapter,we present two dark energy models based on holographic principle in DGP brane-world theory.For lots of models interpreting the accelerating expansion of universe,the modified Chaplygin gas?MCG?model provides a unified model for dark energy and dark matter.The third part in this paper mainly studies the reduced MCG?abbreviated asRMCG?cosmologicalmodel,whichcanbegivenbytheMCG model p?28?A?-B?^-?.The equation of state of the RMCG fluid can be obtained by selecting the parameters??28?-12 in MCG.In the FRW universe containing RMCG fluid,the dark-component models can be achieved by taking the different values of model parameter A.Concretely,we analyze the viabilities of RMCG model by discussing the evolutions of cosmological quantities and the limitations on models from the theories and the observations.It is found that RMCG unified model?A?28?0 or A?28?1?of dark matter and dark energy should be abandoned;the RMCG unified model?A?28?1 3?of dark radiation and dark energy is a good candidate model for cosmic accelerating expansion;For A?27?0,RMCG can realize the features of the dynamical quintessence and phantom dark energy,where the evolution of the universe is not sensitive to the variation of model-parameter values.Furthermore,we study the future singularity of the RMCG universe at finite time for A?27?0.By calculating,it is shown that the RMCG model has no future singularity at finite time for 0?29?A?29?-1.But for A?27?-1,the big rip singularity occurs in the model.