3 research outputs found
Dynamics of dark energy
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 observational
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 nature 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.Comment: 93 pages, 26 figures, Invited Review to be submitted to International
Journal of Modern Physics D; comments are welcome; Additional references
included in response to over 60 comments received. Rewriting of sub-sections
on anthropic principle and gravitational backreaction. New subsections adde
What is needed of a tachyon if it is to be the dark energy?
We study a dark energy scenario in the presence of a tachyon field
with potential and a barotropic perfect fluid. The cosmological
dynamics crucially depends on the asymptotic behavior of the quantity
. If is a constant, which corresponds to
an inverse square potential , there exists one
stable critical point that gives an acceleration of the universe at late times.
When asymptotically, we can have a viable dark energy scenario
in which the system approaches an ``instantaneous'' critical point that
dynamically changes with . If approaches infinity
asymptotically, the universe does not exhibit an acceleration at late times. In
this case, however, we find an interesting possibility that a transient
acceleration occurs in a regime where is smaller than of order
unity.Comment: 11 pages and 3 figures, minor clarifications added; final version to
appear in PR
Accelerated expansion of a universe containing a self-interacting Bose-Einstein gas
Acceleration of the universe is obtained from a model of non-relativistic
particles with a short-range attractive interaction, at low enough temperature
to produce a Bose-Einstein condensate. Conditions are derived for
negative-pressure behavior. In particular, we show that a phantom-accelerated
regime at the beginning of the universe solves the horizon problem,
consistently with nucleosynthesis.Comment: 18 pages, 4 figure