A model-independent assessment of the late-time dark energy density evolution

TL;DR

This paper introduces a model-independent method using Gaussian Processes to reconstruct dark energy density evolution from recent cosmological data, challenging the need for phantom or evolving dark energy models.

Contribution

It proposes a novel, model-independent approach to reconstruct dark energy density directly from data, avoiding parametric biases inherent in traditional EoS parameterizations.

Findings

All models agree with the reconstruction within 95% confidence level.

Largest discrepancy observed for ΛCDM with DESY5 at low redshifts.

Current data do not provide statistically significant evidence for evolving or phantom dark energy.

Abstract

Combined measurements of Baryon Acoustic Oscillations (BAO) from the Dark Energy Spectroscopic Survey (DESI), the Cosmic Microwave Background (CMB) and Type Ia Supernovae (SN Ia), have recently challenged the $\Lambda$-Cold Dark Matter ($\Lambda$CDM) paradigm, indicating potential evidence for a dynamical dark energy component. These results are usually obtained in the context of the dark energy equation-of-state (EoS) parameterizations, generally implying in phantom-crossing at intermediate redshifts. However, a general mapping between these parameterizations that yields approximately the same background observables clouds the inference of the true nature of dark energy in the context of these parametric methods. In this work, we propose a model-independent reconstruction of the dark energy density, which is more directly constrained than its EoS, based on the Gaussian Process (GP) regression method with the use of DESI DR2 BAO data and the Pantheon+, Union3 and DESY5 SN Ia samples. In addition, we perform a statistical comparison between the energy densities of $\Lambda$, a non-phantom thawing quintessence-type dark energy, and the Chevallier-Polarski-Linder parameterization with the reconstructed function. We find that all models agree with the GP reconstruction at 95\% C.L., with the largest discrepancy coming from $\Lambda$CDM with DESY5 at low redshifts. Even in this case, our findings suggest that it may be premature to claim statistically significant evidence for evolving or phantom dark energy with current DESI and SN Ia measurements.