Theoretical Study On Cosmological Evolution And Related Problems Of Tsallis Agegraphic Dark Energy Model With Viscosity

At the end of the 20th century,observations of la supernovae ect.have showed that our universe is speeding up.To explain this acceleration,a kind of mysterious,unknown compo-nent,i.e.,dark energy(DE)is hypothesized based on observations of the universe.It has a strong negative pressure,uniform distribution in the universe,which can make the universe ac-celerated expansion.A number of dark energy models have been proposed in recent years to understand why space-time is accelerating on a cosmic scale.The cosmological constant model(the equation of state is-1 and does not evolve with time)was first proposed by Einstein,which is the simplest dark energy candidate in great agreement with the observed results.But this model also encountered some problems such as the fine tunning itself and coincidence of the model.To solve these puzzles,scientists have put forward a number of dark energy models such as the scalar field DE model,Chaplygin gas(CG)and holographic dark energy(HDE)model and so on.But these models have all different shortcomings,respectively.In this dissertation we mainly study the viscous Tsallis Agegraphic dark energy(TADE)model,which can be used to explain the accelerated expansion of the present universe.The structure of this dissertation is arranged as follows:firstly,the development histo-ry of cosmology and several typical dark energy models are briefly introduced,and then the main work during author' s postgraduate study is showed,which includes the cosmological evolutions and the discussions of related problems for the viscous TADE model.Concretely,in this dissertation under the background of a flat universe,we will firstly discuss the evolu-tionary laws of cosmological quantities such as the density parameter,the state parameter and decelerate parameter ect.for the TADE model,in the no-interaction case and the four interac-tion cases between the DE and dark matter(DM),respectively.The research results show that the universe is not going to happen big rip in the future,but when considering the interactions between DE and DM,the evolutionary trends of cosmological quantities are more accordance with astronomical observations than ones in the no-interaction case and the state parameter can pass through the Phantom divide.Next,on the base of the above discussions we will deeply study the TADE model with viscosity,in the four different interactions between DE and DM,and find that the viscosity can delay the transition from slowdown to speedup for the expand of the universe.Moreover,we will geometrically diagnose the model with the two ways of the statefinder hierarchy and Om diagnosis,and find that the two geometric diagnosis can well differ the four different interactions between DE and DM in the TADE model.Finally,we will perform the linear perturbation analysis of the model,and find that the growth variables and growth factors of DM all show decreasing trends with the increasing redshift z,which in accord with the fact that the universe is accelerating expansion.