1 research outputs found
Dark Matter and Dark Energy
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
times larger than the observed value \la/8\pi G \simeq
10^{-47}GeV. Setting \la 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 \la 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 \atridot/a H^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.Comment: 40 pages, 11 figures, Lectures presented at the Second Aegean Summer
School on the Early Universe, Syros, Greece, September 2003, New References
added Final version to appear in the Proceeding