2014/08/31 by Nobuyoshi KOMATSU, Nobuyoshi Komatsu, Shigeo KIMURA +1
Physics and Astronomy · #Astronomy #Black Holes and Theoretical Physics #Cosmology #Cosmology and Gravitation Theories #Dark energy #Dissipative system #Metric expansion of space #Non-standard cosmology #Physics #Relativity and Gravitational Theory #Theoretical physics #Thermodynamics #Universe #astro-ph.CO #hep-ph
paper · pdf · doi:10.1103/physrevd.90.123516
published as Phys. Rev. D 90, 123516 (2014) · Final version accepted for publication in PRD. References are corrected. [14 pages, 7 figures]
arxiv created 2014/12/12 · openalex publication_date 2014/12/12 · arxiv updated 2014/12/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The bulk viscosity of cosmological fluid and the creation of cold dark matter both result in the generation of irreversible entropy (related to dissipative processes) in a homogeneous and isotropic universe. To consider such effects, the general cosmological equations are reformulated, focusing on a spatially flat matter-dominated universe. A phenomenological entropic-force model is examined that includes constant terms as a function of the dissipation rate ranging from \stackrel\texttildelow\ensuremathμ=0, corresponding to a nondissipative \mathrm\ensuremathΛCDM (lambda cold dark matter) model, to \stackrel\texttildelow\ensuremathμ=1, corresponding to a fully dissipative CCDM (creation of cold dark matter) model. A time-evolution equation is derived for the matter density contrast in order to characterize density perturbations in the present entropic-force model. It is found that the dissipation rate affects the density perturbations even if the background evolution of the late universe is equivalent to that of a fine-tuned pure \mathrm\ensuremathΛCDM model. With increasing dissipation rate \stackrel\texttildelow\ensuremathμ, the calculated growth rate for the clustering gradually deviates from observations, especially at low redshifts. However, the growth rate for low \stackrel\texttildelow\ensuremathμ (less than 0.1) is found to agree well with measurements. A low-dissipation model predicts a smaller growth rate than does the pure \mathrm\ensuremathΛCDM model (for which \stackrel\texttildelow\ensuremathμ=0). More detailed data are needed to distinguish the low-dissipation model from the pure \mathrm\ensuremathΛCDM one.