Model independent reconstruction of cosmological accelerated-decelerated phase

TL;DR

This paper introduces two model-independent methods to constrain the redshifts marking the transition to cosmic acceleration and the equality of dark energy and matter densities, using cosmographic expansions and observational data.

Contribution

It develops novel, model-independent techniques to estimate key cosmological transition redshifts directly from data, avoiding assumptions of specific dark energy models.

Findings

Lambda CDM predictions are slightly confirmed at 1σ

Dark energy cannot be excluded at 2σ confidence

Linear correlation between transition and equivalence redshifts

Abstract

We propose two model independent methods to obtain constraints on the transition and equivalence redshifts $z_{tr}$, $z_{eq}$. In particular, we consider $z_{tr}$ as the onset of cosmic acceleration, whereas $z_{eq}$ the redshift at which the densities of dark energy and pressureless matter are equated. With this prescription, we expand the Hubble and deceleration parameters up to two hierarchical orders and show a linear correlation between transition and equivalence, from which we propose exclusion plots where $z_{eq}$ is not allowed to span. To this end, we discuss how to build up cosmographic expansions in terms of $z_{tr}$ and compute the corresponding observable quantities directly fitting the luminosity and angular distances and the Hubble rate with cosmic data. We make our computations through Monte Carlo fits involving type Ia supernova, baryonic acoustic oscillation and Hubble most recent data catalogs. We show at $1\sigma$ confidence level the $\Lambda$CDM predictions on $z_{tr}$ and $z_{eq}$ are slightly confirmed, although at $2\sigma$ confidence level dark energy expectations cannot be excluded. Finally, we theoretically interpret our outcomes and discuss possible limitations of our overall approach.