5 Dark Matter and Dark Energy

Abstract

Abstract. I briefly review our current understanding of dark matter and dark energy. The first part of this paper focusses on issues pertaining to dark matter including observational evidence for its existence, current constraints and the 'abundance of substructure' and 'cuspy core' issues which arise in CDM. I also briefly describe MOND. The second part of this review focusses on dark energy. In this part I discuss the significance of the cosmological constant problem which leads to a predicted value of the cosmological constant which is almost 10 123 times larger than the observed value Λ/8πG ≃ 10 −47 GeV 4 . Setting Λ to this small value ensures that the acceleration of the universe is a fairly recent phenomenon giving rise to the 'cosmic coincidence' conundrum according to which we live during a special epoch when the density in matter and Λ are almost equal. Anthropic arguments are briefly discussed but more emphasis is placed upon dynamical dark energy models in which the equation of state is time dependent. These include Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model independent methods to determine the cosmic equation of state and the Statefinder diagnostic are also discussed. The Statefinder has the attractive property ... a /aH 3 = 1 for LCDM, which is helpful for differentiating between LCDM and rival dark energy models. The review ends with a brief discussion of the fate of the universe in dark energy models.

Interactive mixture of inhomogeneous dark fluids driven by dark energy: a dynamical system analysis

“…However, for α < 0 (energy transfer from CDM to DE) the DE density became negative in phase space regions around the past attractor (irrespective of initial conditions), thus signalling an unphysical past evolution that is inconsistent with all observational data. This problem was already noticed in the literature with this type of CDM-DE mixtures based on FLRW metrics [1,2,7,8].…”

“…We have not include this source in (3) because, as shown in Appendix A, it does not introduce significant changes in the qualitative behaviour of the solutions. 2 Notice that A q is related to the proper volume average of A with weight factor √ 1 + K . See comprehensive discussion in [35].…”

“…Current observational evidence supports the existence of an accelerated cosmic expansion, likely driven by an unknown form of matter-energy, generically denoted "dark energy" (DE), and usually described by suitable scalar fields or (phenomenologically) as a fluid with negative pressure [1][2][3][4]. Observations also point to the existence of cold dark matter (CDM) clustering around galactic halos, usually described in cosmological scales by pressure-less dust, while ordinary visible matter (baryons, electrons and neutrinos) and phoa e-mail: gizquierdos@uaemex.mx tons (radiation) comprise less than 5% of the total contents of cosmic mass-energy.…”

“…Several models of coupled dark sources can also be found in the literature motivated by particle physics, thermodynamics, etc. [1,2,[7][8][9][10][11].…”

“…The interplay of local and cosmic dynamics at all scales must comply with the observed anisotropy of the Cosmic Microwave Background (CMB) [1][2][3][4]. Evidently, this dynamics depends on the assumptions made on DE and CDM, which leads to a model dependent power spectrum that should be contrasted with observations at large scales and in structure formation (from data and from numerical simulations).…”