4,437 research outputs found
Dark energy, matter creation and curvature
The most studied way to explain the current accelerated expansion of the
universe is to assume the existence of dark energy; a new component that fill
the universe, does not clumps, currently dominates the evolution, and has a
negative pressure. In this work I study an alternative model proposed by Lima
et al. \cite{lima96}, which does not need an exotic equation of state, but
assumes instead the existence of gravitational particle creation. Because this
model fits the supernova observations as well as the CDM model, I
perform in this work a thorough study of this model considering an explicit
spatial curvature. I found that in this scenario we can alleviate the cosmic
coincidence problem, basically showing that these two components, dark matter
and dark energy, are of the same nature, but they act at different scales. I
also shown the inadequacy of some particle creation models, and also I study a
previously propose new model that overcome these difficulties.Comment: 6 pages, 4 figures. Accepted for publication in EPJC. arXiv admin
note: substantial text overlap with arXiv:0812.386
Asymmetry in the reconstructed deceleration parameter
We study the orientation dependence of the reconstructed deceleration
parameter as a function of redshift. We use the Union 2 and Loss datasets, by
using the well known preferred axis discussed in the literature, finding the
best fit reconstructed deceleration parameter. We found that a low redshift
transition of the reconstructed is clearly absent in one direction and
amazingly sharp in the opposite one. We discuss the possibility that such a
behavior can be associated with large scale structures affecting the data.Comment: 9 pages, 12 figure
Testing a dissipative kinetic k-essence model
In this work, we present a study of a purely kinetic k-essence model,
characterized basically by a parameter in presence of a bulk
dissipative term, whose relationship between viscous pressure and energy
density of the background follows a polytropic type law , where , in principle, is a parameter without
restrictions. Analytical solutions for the energy density of the k-essence
field are found in two specific cases: and
, and then we show that these solutions posses the
same functional form than the non-viscous counterpart. Finally, both approach
are contrasted with observational data from type Ia supernova, and the most
recent Hubble parameter measurements, and therefore, the best values for the
parameters of the theory are founds.Comment: 9 pages, 5 figures, accepted in EPJ
Testing cosmic acceleration for parameterizations using measurements in galaxy clusters
In this paper we study the cosmic acceleration for five dynamical dark energy
models whose equation of state varies with redshift. The cosmological
parameters of these models are constrained by performing a MCMC analysis using
mainly gas mass fraction, , measurements in two samples of galaxy
clusters: one reported by Allen et al. (2004), which consists of points
spanning the redshift range , and the other by Hasselfield et al.
(2013) from the Atacama Cosmology Telescope survey, which consists of data
points in the redshift range . In addition, we
perform a joint analysis with the measurements of the Hubble parameter ,
baryon acoustic oscillations and the cosmic microwave background radiation from
WMAP and Planck measurements to estimate the equation of state parameters. We
obtained that both samples provide consistent constraints on the
cosmological parameters. We found that the data is consistent at the
confidence level with a cosmic slowing down of the acceleration at
late times for most of the parameterizations. The constraints of the joint
analysis using WMAP and Planck measurements show that this trend disappears. We
have confirmed that the probe provides competitive constraints on the
dark energy parameters when a is assumed.Comment: 21 pages, 8 Tables, 11 Figures, accepted for publication in MNRA
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