Cosmological Analysis Of The Chaplygin Gas Model In The DGP Braneworld

The cosmic observation data show that at this stage,the universe is accelerating expansion.Whether in theory or experimental observation,the accelerated expansion of the universe is a frontier issue in cosmology.Over the years,scientists have found two explanations for the accelerated expansion of the universe by modifying the material and geometric terms of the Einstein field equation:the first explanation is to introduce dark energy with negative pressure into the cosmic components and make full use of its repulsive gravitational effect;The second explanation is to modify the space-time geometry of the universe,that is,to produce a new gravitational theory.The gravitational theory mainly introduced in this thesis is DvaliGabadadze-Porrati(DGP)braneworld theory.In this thesis,we consider the Friedmann-Robertson-Walker(FRW)universe full of interacting dark energy and dark matter.Assuming that the Hubble horizon is IR cutoff,we study the cosmic evolution properties and related thermodynamic problems of the generalized Chaplygin gas model(GCG)and the modified Chaplygin gas model(MCG)in the self-accelerating and normal branches of DGP braneworld.The main contents of this paper are as follows:firstly,this paper briefly describes the current two explanations for the accelerated expansion of the universe,and mainly introduces the cosmological constant model,GCG model,MCG model and DGP braneworld theory.Secondly,the cosmological evolution of GCG model and MCG model under self-accelerating branch and normal branch of DGP braneworld is mainly studied,and the effects of state parameter and model parameters on the evolution law of energy density parameters and deceleration parameter of the model are analyzed.The results show that the GCG model and MCG model in the DGP braneworld are in line with the evolution law of the current universe.They not only realize the transformation of the main components of the universe from matter to energy,but also reflect that the universe is in the stage of accelerated expansion.In addition,statefinder hierarchy diagnosis and Om diagnosis are carried out for the model.When different state parameters and model parameters are adopted,the dark energy model and ACDM model can be better distinguished statefinder hierarchy diagnosis shows that the model will show evolutionary behavior similar to ACDM model in the future,and Om diagnosis can effectively eliminate the degeneracy of the model in all stages of cosmic evolution.Finally,this paper discusses the thermodynamic properties of GCG model and MCG model with interaction under the framework of DGP braneworld,by drawing images,it is verified that the two models meet the second law of generalized thermodynamics and can well meet the effectiveness of the cosmic heat balance.