Omnipotent dark energy: A phenomenological answer to the Hubble tension

TL;DR

This paper proposes omnipotent dark energy models with nonmonotonic, negative densities and PDL crossings to address the Hubble tension, confirming their effectiveness with extended datasets and uncovering the role of negative DE densities.

Contribution

It introduces and tests a class of dark energy models with negative densities and PDL crossings, demonstrating their potential to alleviate the Hubble tension.

Findings

Negative DE densities are crucial in reducing the Hubble tension.

The model achieves H0=70.05 ± 0.64 km/s/Mpc, easing the Hubble tension.

Positive correlation between H0 and the transition scale a_p was confirmed.

Abstract

This paper introduces the class of omnipotent dark energy (DE) models characterized by nonmonotonic energy densities that are capable of attaining negative values with corresponding equation of state parameters featuring phantom divide line (PDL) crossings and singularities. These nontrivial features are phenomenologically motivated by findings of previous studies that reconstruct cosmological functions from observations, and the success of extensions of $\Lambda$CDM, whose actual or effective DE density is omnipotent, in alleviating the observational discordance within $\Lambda$CDM. As an example, we focus on one embodiment of omnipotent DE, viz., the DE parametrization introduced in Di Valentino et al. [Dark energy with phantom crossing and the H0 tension, Entropy 23, 404 (2021)] (DMS20). By updating and extending the datasets used in the original paper where it was introduced, we confirm the effectiveness of DMS20 in alleviating the observational discrepancies. Additionally, we uncover that its negative DE density feature, importance of which was not previously investigated, plays a crucial role in alleviating the tensions, along with the PDL crossing feature that the parametrization presupposes. In particular, we find that there is a positive correlation between the $H_0$ parameter and the scale ($a_p$) at which DE density transitions from negative to positive, in agreement with previous studies that incorporate this transition feature. For our full dataset, the model yields $H_0=70.05 \pm 0.64$ (68% CL) relaxing the $H_0$ tension with a preference of crossing to negative DE densities ($a_p>0$ at 99% CL), along with the constraint $a_m=0.922^{+0.041}_{-0.035}$ on the scale of the presupposed PDL crossing.