Some Issues On F(T) Cosmology

Observational data coming from the type la supernovae surveys, large scale struc-ture and cosmic microwave anisotropy spectrum indicate that the expansion of our present universe is accelerating rather than slowing down. This cosmic acceleration can not be explained by the four known fundamental interactions in the standard models, which is the greatest challenge today in the modern physics. The proposals that have been put forward to explain this observed phenomenon can basically be classified into two categories:one is to assume that in the framework of Einstein’s general relativity, an exotic component with negative pressure called dark energy is necessary to explain this observed phenomenon. Another alternative to account for the current accelerating cosmic expansion is to modify the gravitational action. At present there exists a lot of work based on these two approaches. Moreover, the other interesting issue in modern cosmology is the thermodynamical description of the accelerating universe driven by dark energy or modified gravity. In this paper, we discuss one kind of modified gravity and consider its thermodynamics. In chap-ter 2, we give a brief review of the standard cosmology, including the theories, the observations and the cosmological constant problem. In chapter 3, we discuss a kind of models in which the gravity is modified to f(T) theory, we focus on f(T) gravity with non-minimal torsion-matter coupling extension. Using the observational data mentioned above, we establish two concrete f(T) models with a non-minimal torsion-matter coupling and perform a joint analysis. We obtain the best fitting values of the parameters for these two models and discuss their cosmological implication-s. In chapter 4.we mainly discuss thermodynamics of f(T) theory with non-minimal torsion-matter coupling extension.We give out the first law and the second law of thermodynamics with the equilibrium and the non-equilibrium description and check the validity of the generalized second law of thermodynamics for two concrete f(T) models.Chapter 5 is the summary and outlook.