The Effective Potential Of Quintessence And The Brans-Dicke Coupling

In the introduction of this thesis,the research background and the current research situations of quintessence model and the large scale Lorentz violation model is introduced.In the second chapter,the quintessence model is introduced,and it is explained that the quintessence field can cause accelerated expansion of the universe.In the third chapter,the Brans-Dicke theory is introduced,and the significance of introducing non-minimum Brans-Dicke coupling in the quintessence field is explained.In the fourth chapter,the large-scale Lorentz violation model is introduced,and the effective cosmological constant after considering the large-scale Lorentz violation is defined.In the fifth chapter,we give the evolution of the effective cosmological constant,and the effective vacuum energy density contributed by non-trivial contortion and the bare vacuum energy density can be viewed as the energy density of the auxiliary quintessence field potential.We find that the negative bare vacuum energy density from string landscape leads to a monotonically decreasing quintessence potential while the positive one from swampland leads to the meta stable or stable de Sitter like potential.Moreover,the non-trivial Brans-Dicke like coupling between quintessence field and gravitation field is necessary in the latter case.