High-redshift investigation on the dark energy equation of state

Abstract

The understanding of the accelerated expansion of the Universe poses one of the most fundamental questions in physics and cosmology today. Whether or not the acceleration is driven by some form of dark energy, and in the absence of a well-based theory to interpret the observations, many models have been proposed to solve this problem, both in the context of General Relativity and alternative theories of gravity. Actually, a further possibility to investigate the nature of dark energy lies in measuring the dark energy equation of state (EOS) , w, and its time (or redshift) dependence at high accuracy. However, since w(z) is not directly accessible to measurement, reconstruction methods are needed to extract it reliably from observations. Here we investigate different models of dark energy, described through several parametrizations of the EOS. Our high-redshift analysis is based on the Union2 Type Ia Supernovae (SNIa) data set, the Hubble diagram constructed from some Gamma Ray Bursts (GRBs) luminosity distance indicators, and Gaussian priors on the distance from the Baryon Acoustic Oscillations (BAO), and the Hubble constant h (these priors have been included in order to help break the degeneracies among model parameters). To perform our statistical analysis and to explore the probability distributions of the EOS parameters we use the Markov Chain Monte Carlo Method (MCMC). It turns out that the dark energy equation of state is evolving for all the parametrizations that we considered. We finally compare our results with the ones obtained by previous cosmographic analysis performed on the same astronomical datasets, showing that the latter ones are sufficient to test and compare the new parametrizations.

Cosmological perfect fluids in higher-order gravity

“…However, this statement is phenomenological and has to be compared with observations. In particular, cosmography can be an efficient tool to discriminate among concurring models as discussed, for example, in [22][23][24][25].…”

Einstein, Planck and Vera Rubin: Relevant Encounters Between the Cosmological and the Quantum Worlds

“…This correlation can be properly calibrated and allows us to standardize the GRBs as a distance indicators in a way similar to that used for the Phillips relation concerning SNeIas ( [82] and reference therein). Then, once the correlation between E p,i and E iso is calibrated, it is possible to estimate the luminosity distance d L (z, θ) by using Equation 3, and therefore to build up the Gamma Ray Burst Hubble diagram [83][84][85][86][87]. Furthermore, Eisenstein et al (2005) introduced BAOs as standard rulers [88], Chavez (2016) used HII galaxies [89], and Negrete et al (2017) used extreme quasars [90].…”

“…assuming some analytical form of w as function of z [83]. Otherwise, we can follow a cosmographic approach relying upon quantities that are not model dependent.…”

Investigating Dark Energy Equation of State With High Redshift Hubble Diagram

“…This happens, for instance, in extended theories of gravity (Demianski et al, 2006(Demianski et al, , 2008Piedipalumbo et al, 2012Piedipalumbo et al, , 2015, or in an interacting quintessence cosmology (Piedipalumbo et al, 2020): actually in the generalized Friedman equations, that drive the dynamics of these models, we can identify effective density and pressure terms, and define effective EOS. Understanding from the data whether or not the dark energy EOS is constant, independently of any assumptions on its nature, is, therefore, a daunting yet rewarding task of probing the evolution of dark energy (Piedipalumbo et al, 2014).…”