Reconstruction of the Cosmic Equation of State for High Redshift

We investigate the possibilities of reconstructing the cosmic equation of state (EoS) for high redshift. In order to obtain general results, we use two model-independent approaches. The first reconstructs the EoS using comoving distance and the second makes use of the Hubble parameter data. To implement the first method, we use a recent set of Gamma-Ray Bursts (GRBs) measures. To implement the second method, we generate simulated data using the Sandage-Loeb ($SL$) effect; for the fiducial model, we use the $\Lambda CDM$ model. In both cases, the statistical analysis is conducted through the Gaussian processes (non-parametric). In general, we demonstrate that this methodology for reconstructing the EoS using a non-parametric method plus a model-independent approach works appropriately due to the feasibility of calculation and the ease of introducing a priori information ($H_ {0}$ and $\Omega_{m0}$). In the near future, following this methodology with a higher number of high quality data will help obtain strong restrictions for the EoS.Comment: 9 pages, 5 figure

Vacuum effective action and inflation

We consider vacuum quantum effects in the Early Universe, which may lead to inflation. The inflation is a direct consequence of the supposition that, at high energies, all the particles can be described by the weakly interacting, massless, conformally invariant fields. We discuss, from the effective field theory point of view, the stability of inflation, transition to the FRW solution, and also possibility to study metric and density perturbations.Comment: 6 pages, LaTeX, no figures. Contribution to the Proceedings of the X Jorge Andre Swieca school in Particles and Fields. To be published in World Scientifi

Anomaly-Induced Effective Action and Inflation

In the early Universe matter can be described as a conformal invariant ultra-relativistic perfect fluid, which does not contribute, on classical level, to the evolution of the isotropic and homogeneous metric. If we suppose that there is some desert in the particle spectrum just below the Planck mass, then the effect of conformal trace anomaly is dominating at the corresponding energies. With some additional constraints on the particle content of the underlying gauge model (which favor extended or supersymmetric versions of the Standard Model rather than the minimal one), one arrives at the stable inflation. We review the model and report about the calculation of the gravitational waves on the background of the anomaly-induced inflation. The result for the perturbation spectrum is close to the one for the conventional inflaton model, and is in agreement with the existing Cobe data (see also [hep-th/0009197]).Comment: 4 pages, LaTeX. Contribution to the Proceedings of the EuroConference on Frontiers in Particle Astrophysics and Cosmology, 30 September - 5 October 2000. San Feliu, Spai

Observational constraints on Rastall's cosmology

Rastall's theory is a modification of General Relativity, based on the non-conservation of the stress-energy tensor. The latter is encoded in a parameter $\gamma$ such that $\gamma = 1$ restores the usual $\nabla_\nu T^{\mu\nu} = 0$ law. We test Rastall's theory in cosmology, on a flat Robertson-Walker metric, investigating a two-fluid model and using the type Ia supernovae Constitution dataset. One of the fluids is pressureless and obeys the usual conservation law, whereas the other is described by an equation of state $p_x = w_x\rho_x$, with $w_x$ constant. The Bayesian analysis of the Constitution set does not strictly constrain the parameter $\gamma$ and prefers values of $w_x$ close to -1. We then address the evolution of small perturbations and show that they are dramatically unstable if $w_x \neq -1$ and $\gamma \neq 1$, i.e. General Relativity is the favored configuration. The only alternative is $w_x = -1$, for which the dynamics becomes independent from $\gamma$.Comment: Latex file, 14 pages, 6 figures in eps format. Substantial modifications performed, main conclusions change