Cosmology Thermodynamic Analysis: The Generalized Thermodynamic Second Theorem And The Interaction Between Dark Energy Model

The observational data showing that our universe is experiencing an accelerated expansion. Under the framework of Standard Cosmology,the concept of dark energy is introduced in order to explain the phenomena of the accelerated expansion.However, the nature of the so-called dark energy still remains a complete mystery,except for the fact that it has negative pressure.Inspired by the profound connection between the black hole physics and thermodynamics,there has been some deep thinking on the relation between gravity and thermodynamics in general for a long time.Many studies on the connection between gravity and thermodynamics has been investigated in various gravity theories[5].In the cosmological context,it is shown that the differential form of the Friedmann equation in the FRW universe can be written in the form of the first law of thermodynamics on the apparent horizon[6].The profound connection provides a therrnodynamical interpretation of gravity which makes it interesting to explore the cosmological properties through thermodynamics.The dissertation is devoted to the study of the second law of thermodynamics with different models.It is organized as follows.In chapter one we present the background introduction,which is made up of two parts:the interaction between dark matter and dark energy;the second law of thermodynamics.In chapter two we have studied the generalized second law of thermodynamics in the accelerating universe.It is shown that in the accelerating universe the generalized second law of thermodynamics holds only in the case where the enveloping surface is the apparent horizon,but not in the case of the event horizon.It might be therefore, suggest that event horizon is not a physical boundary from the point of view of thermodynamics.In chapter three we have discussed the mutual interaction between the dark sectors (dark matter and dark energy) of the Universe by resorting to the extended thermodynamics of ineversible processes.The result shows that the interaction between the dark sectors should not be negligible as a byproduct,the present dark matter temperature results not extremely small and can meet the independent estimate of the temperature of the gas of sterile neutrinos.We have used supernova type Ia data in both works.