2006/09/26 by Y. Zhang, Y Zhang, T. Y. Xia +3 · 6 citations
Physics and Astronomy · #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Dark energy #Dark matter #Equation of state #Pulsars and Gravitational Waves Research #Radiation #Redshift #Scalar field dark matter #Scaling #Supernova #Universe #gr-qc
paper · pdf · doi:10.1088/0264-9381/24/13/011
published as Class.Quant.Grav.24:3309-3338,2007 · 24 pages, 18 figures
arxiv created 2006/09/26 · openalex publication_date 2007/06/18 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The coincidence problem is studied for the dark energy model of effective Yang–Mills condensate (YMC) in a flat expanding universe during the matter-dominated stage. The YMC energy ρ y ( t ) is taken to represent the dark energy, which is coupled either with the matter ρ m ( t ), or with both the matter and the radiation components ρ r ( t ). The effective YM Lagrangian is completely determined by the quantum field theory up to 1-loop order with an energy scale ∼10 −3 eV as a model parameter, and for each coupling, there is an extra model parameter. We have studied extensively the coupling models: the YMC decaying into the matter and the radiation; or vice versa the matter and radiation decaying into the YMC. It is found that, starting from the equality of radiation-matter ρ mi = ρ ri , for a wide range of initial conditions of ρ yi = (10 −10 , 10 −2 )ρ mi , the models have a scaling solution during the early stages, and the YMC levels off and becomes dominant at late time, and the present state with Ω y ≃ 0.7, Ω m ≃ 0.3 and Ω r ≃ 10 −5 is always achieved. If the YMC decays into a component, then this component also levels off later and approaches a constant value asymptotically, and the equation of state (EoS) of the YMC w y = ρ y / p y crosses over −1 and takes the value w y ≃ −1.1 at z = 0. If the matter and radiation decay into the YMC, then ρ m ( t ) ∝ a ( t ) −3 and ρ r ( t ) ∝ a ( t ) −4 approximately for all the time, and w y approaches −1 but does not cross over −1. We have also demonstrated that, at t → ∞ , the coupled dynamics for (ρ y ( t ), ρ m ( t ), ρ r ( t )) is a stable attractor. Therefore, under generic circumstances, the existence of the scaling solution during the early stages and the subsequential exit from the scaling regime around z ≃ (0.3–0.5) are inevitable. Thus the coincidence problem can be naturally solved in the YMC dark energy models.