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