2009/10/31 by Ahmad Sheykhi · 3 citations
Physics and Astronomy · #Apparent horizon #Astronomy #Astrophysics #Cosmology #Cosmology and Gravitation Theories #Cutoff #Dark Matter and Cosmic Phenomena #Dark energy #Dark fluid #Dark matter #Event horizon #Galaxies: Formation, Evolution, Phenomena #Horizon #Metric expansion of space #Particle horizon #Physics #Quantum mechanics #Theoretical physics #Universe #hep-th
paper · pdf · doi:10.1088/0264-9381/27/2/025007
published as Class.Quant.Grav.27:025007,2010 · 11 pages, Accepted in Class. Quantum. Grav
arxiv created 2009/11/29 · openalex publication_date 2009/12/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
As soon as an interaction between holographic dark energy and dark matter is taken into account, the identification of an IR cutoff with the Hubble radius H −1 , in a flat universe, can simultaneously drive accelerated expansion and solve the coincidence problem. Based on this, we demonstrate that in a non-flat universe the natural choice for the IR cutoff could be the apparent horizon radius, . We show that any interaction of dark matter with holographic dark energy, whose infrared cutoff is set by the apparent horizon radius, implies an accelerated expansion and a constant ratio of the energy densities of both components thus solving the coincidence problem. We also verify that for a universe filled with dark energy and dark matter, the Friedmann equation can be written in the form of the modified first law of thermodynamics, d E = T h d S h + W d V , at the apparent horizon. In addition, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon. These results hold regardless of the specific form of dark energy and interaction term. Our study might reveal that in an accelerating universe with spatial curvature, the apparent horizon is a physical boundary from the thermodynamical point of view.