Cosmological degeneracy versus cosmography: a cosmographic dark energy model

TL;DR

This paper employs cosmography to parameterize and constrain dark energy evolution without assuming a specific form, providing a model that allows for a slight evolution of dark energy over time.

Contribution

It introduces a self-consistent cosmographic dark energy model that independently bounds matter and dark energy densities without assuming a specific dark energy form.

Findings

Dark energy may evolve slightly over time.

The model constrains dark energy parameters using Monte Carlo methods.

Results are consistent with a cosmological constant at present.

Abstract

In this work we use cosmography to alleviate the degeneracy among cosmological models, proposing a way to parameterize matter and dark energy in terms of cosmokinematics quantities. The recipe of using cosmography allows to expand observable quantities in Taylor series and to directly compare those expansions with data. We adopt this strategy and we propose a fully self-consistent parametrization of the total energy density driving the late time universe speed up. Afterwards, we describe a feasible \emph{cosmographic dark energy model}, in which matter is fixed whereas dark energy evolves by means of the cosmographic series. Our technique provides robust constraints on cosmokinematic parameters, permitting one to separately bound matter from dark energy densities. Our cosmographic dark energy model turns out to be one parameter only, but differently from the $\Lambda$CDM paradigm, it does not contain ansatz on the dark energy form. In addition, we even determine the free parameter of our model in suitable $1\sigma$ intervals through Monte Carlo analyses based on the Metropolis algorithm. We compare our results with the standard concordance model and we find that our treatment seems to indicate that dark energy slightly evolves in time, reducing to a pure cosmological constant only as $z\rightarrow0$.