Dynamics of dark energy

ln 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. ln 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 la 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.

by Edmund J. Copeland, M. Sami, and Shinji Tsujikawa.

Prof M Sami,Department of theoretical physics,Jamai milla islamia, New Delhi,India.