Theoretical Studies On Agegraphic Dark Energy Model

Since in1998two supernovae observation groups independently found that our uni-verse is undergoing an accelerated expansion at the present stage, cosmological constant and dark energy problems have been one of the most important issues in the research of physics and cosmology. In the introduction of this thesis, the research background of dark energy is introduced and the current research situations are reviewed. In the second chapter, beginning with the discussion on the cosmological dynamics, several in-terpretations about the accelerating expansion of the universe are reviewed, and these interpretations include the cosmological constant model, dynamics scalar field dark en-ergy model (including quintessence, phantom and quintom), holographic dark energy model and modified gravity theory. In the third chapter, we put emphasis on studying the new agegraphic dark energy model in the framework of Brans-Dicke theory. The agegraphic dark energy models were proposed, by considering the famous uncertainty relation in quantum mechanics together with the gravitational effect in general relativity. In the framework of the Brans-Dicke theory, we mainly investigate the dynamical evo-lution behavior of new agegraphic dark energy model, derive concrete expression forms about the density parameter, equation of state parameter and the deceleration parameter of the universe for the new agegraphic dark energy, and find that the agegraphic dark en-ergy can realize quintom-like behavior, namely the equation of state parameter can cross-1during the evolutionary process. We compare the evolution of the agegraphic dark energy model in the framework of the Brans-Dicke theory with that in the Einstein’s the-ory. In addition, we discuss evolution behavior of the new agegraphic dark energy model with interaction in the framework of the Brans-Dicke theory. Besides, we investigate the possible theoretical constraint on the parameter n of the agegraphic quintessence model by considering the requirement of the weak gravity conjecture that the variation of the quintessence scalar field Φ should be less than the Planck mass Mp. We obtain the theo-retical upper bound n<2.5that is inconsistent with the current observational constraint result2.637<n<2.983(95.4%CL). The possible implications of the tension between observational and theoretical constraint results are discussed.