5,731 research outputs found
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
() effect; for the fiducial model, we use the 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 ( and ). 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 such that restores the usual 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 , with constant. The Bayesian analysis of the
Constitution set does not strictly constrain the parameter and prefers
values of close to -1. We then address the evolution of small
perturbations and show that they are dramatically unstable if and
, i.e. General Relativity is the favored configuration. The only
alternative is , for which the dynamics becomes independent from
.Comment: Latex file, 14 pages, 6 figures in eps format. Substantial
modifications performed, main conclusions change
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