Dynamics of dark energy Edmund J. Copeland,1 M. Sami,2, 3 and Shinji Tsujikawa4 1School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom Email:
[email protected] 2Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi, India 3Department of Physics, Jamia Millia Islamia, New Delhi, India Email:
[email protected];
[email protected] 4Department of Physics, Gunma National College of Technology, Gunma 371-8530, Japan Email:
[email protected] (Dated: February 1, 2008) In this paper we review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating Universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observa- tional evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the na- ture of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.