Abstract
The problem of reproducing dark energy effects is reviewed here with particular interest devoted to cosmography. We summarize some of the most relevant cosmological models, based on the assumption that the corresponding barotropic equations of state evolve as the universe expands, giving rise to the accelerated expansion. We describe in detail the ΛCDM (Λ-Cold Dark Matter) and ωCDM models, considering also some specific examples, e.g., Chevallier–Polarsky–Linder, the Chaplygin gas and the Dvali–Gabadadze–Porrati cosmological model. Finally, we consider the cosmological consequences of f(R) and f(T) gravities and their impact on the framework of cosmography. Keeping these considerations in mind, we point out the model-independent procedure related to cosmography, showing how to match the series of cosmological observables to the free parameters of each model. We critically discuss the role played by cosmography, as a selection criterion to check whether a particular model passes or does not present cosmological constraints. In so doing, we find out cosmological bounds by fitting the luminosity distance expansion of the redshift, z, adopting the recent Union 2.1 dataset of supernovae, combined with the baryonic acoustic oscillation and the cosmic microwave background measurements. We perform cosmographic analyses, imposing different priors on the Hubble rate present value. In addition, we compare our results with recent PLANCK limits, showing that the ΛCDM and ωCDM models seem to be the favorite with respect to other dark energy models. However, we show that cosmographic constraints on f(R) and f(T) cannot discriminate between extensions of General Relativity and dark energy models, leading to a disadvantageous degeneracy problem.
Highlights
General Relativity (GR) is today considered a cornerstone of theoretical physics, well supported by a wide number of experiments, in particular, the Solar System ones [1,2]
We reviewed the problem of dark energy (DE) through the use of the cosmography of the universe
We considered cosmography as a tool to select among competing models, showing that cosmography is, at most, a selection criterion to discriminate which model works fairly well over others
Summary
General Relativity (GR) is today considered a cornerstone of theoretical physics, well supported by a wide number of experiments, in particular, the Solar System ones [1,2]. The aim is to reconstruct the EoS of DE, by demanding that the barotropic factor evolves as the universe expands and comparing it with cosmological data at different stages of the universe’s evolution This prescription is due to the fact that the form of ω(z) is not defined a priori, and so, one may reconstruct its evolution by bounding ω(z) and its derivatives, through the use of current observations only [46,47,48]. A procedure that directly compares cosmological observables in terms of data, instead of cosmological models with data, should guarantee improved constraints, being capable of discarding the models that do not match the corresponding experimental limits In this regard, the well-known approach of cosmography has increased its importance during this time, becoming a relevant model-independent technique to fix cosmological constraints on late time cosmology.
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