The implications of an extended dark energy cosmology with massive neutrinos for cosmological tensions

TL;DR

This paper investigates how extended dark energy models with massive neutrinos impact cosmological tensions, finding that neutrino masses around 0.4 eV can alleviate some discrepancies but do not fully resolve the H0 tension, especially when all data are considered.

Contribution

It introduces a comprehensive analysis combining dark energy extensions and massive neutrinos, revealing persistent H0 tension and the potential role of negative dark energy densities.

Findings

Neutrino mass sum around 0.4 eV alleviates S8 tension.

Residual H0 tension remains at ~1.9σ with all datasets.

Negative dark energy densities near z~2.35 are favored, possibly indicating systematics.

Abstract

We perform a comprehensive analysis of the most common early- and late-Universe solutions to the $H_0$, Ly-$\alpha$, and $S_8$ discrepancies. When considered on their own, massive neutrinos provide a natural solution to the $S_8$ discrepancy at the expense of increasing the $H_0$ tension. If all extensions are considered simultaneously, the best-fit solution has a neutrino mass sum of $\sim 0.4$ eV, a dark energy equation of state close to that of a cosmological constant, and no additional relativistic degrees of freedom. However, the $H_0$ tension, while weakened, remains unresolved. Motivated by this result, we perform a non-parametric reconstruction of the evolution of the dark energy fluid density (allowing for negative energy densities), together with massive neutrinos. When all datasets are included, there exists a residual $\sim1.9\sigma$ tension with $H_0$. If this residual tension remains in the future, it will indicate that it is not possible to solve the $H_0$ tension solely with a modification of the late-Universe dynamics within standard general relativity. However, we do find that it is possible to resolve the tension if either galaxy BAO or JLA supernovae data are omitted. We find that \textit{negative} dark energy densities are favored near redshift $z\sim2.35$ when including the Ly-$\alpha$ BAO measurement (at $\sim 2\sigma$). This behavior may point to a negative curvature, but it is most likely indicative of systematics or at least an underestimated covariance matrix. Quite remarkably, we find that in the extended cosmologies considered in this work, the neutrino mass sum is always close to $0.4$ eV regardless of the choice of external datasets, as long as the $H_0$ tension is solved or significantly decreased.