42 research outputs found
Nonparametric reconstruction of the Om diagnostic to test LCDM
Cosmic acceleration is usually related with the unknown dark energy, which
equation of state, w(z), is constrained and numerically confronted with
independent astrophysical data. In order to make a diagnostic of w(z), the
introduction of a null test of dark energy can be done using a diagnostic
function of redshift, Om. In this work we present a nonparametric
reconstruction of this diagnostic using the so-called Loess-Simex factory to
test the concordance model with the advantage that this approach offers an
alternative way to relax the use of priors and find a possible 'w' that
reliably describe the data with no previous knowledge of a cosmological model.
Our results demonstrate that the method applied to the dynamical Om diagnostic
finds a preference for a dark energy model with equation of state w =-2/3,
which correspond to a static domain wall network.Comment: 10 pages, 5 figures, 2 table
Some remarks on the observational constraints on the self-interacting scalar field model for dark energy
The dark energy component of the cosmic budget is represented by a
self-interacting scalar field. The violation of the null energy condition is
allowed. Hence, such component can also represent a phantom fluid. The model is
tested using supernova type Ia and matter power spectrum data. The supernova
test leads to preferred values for configurations representing the phantom
fluid. The matter power spectrum constraints for the dark energy equation of
state parameter are highly degenerated. In both cases, values for the equation
of state parameter corresponding to the phantom fluid are highly admitted if no
particular prior is used.Comment: Latex file, 12 pages, 12 figures in eps forma
Scalar models for the unification of the dark sector
We review the difficulties of the generalized Chaplygin gas model to fit
observational data, due to the tension between background and perturbative
tests. We argue that such issues may be circumvented by means of a
self-interacting scalar field representation of the model. However, this
proposal seems to be successful only if the self-interacting scalar field has a
non-canonical form. The latter can be implemented in Rastall's theory of
gravity.Comment: Latex file, 8 pages, 3 figures in eps format. To appear in the
proceedings of the CosmoSul conference, held in Rio de Janeiro, Brazil, 01-05
august of 201