When One-Parameter Dark Energy Makes Neutrinos Physical Again

TL;DR

This paper explores whether simple one-parameter dark energy models can resolve the issue of negative neutrino mass sums in cosmological data, finding that certain models with phantom behavior and crossing w=-1 are sufficient.

Contribution

It demonstrates that specific one-parameter dark energy equations of state can make neutrino masses positive without needing more complex models.

Findings

Certain one-parameter DE EoS models suffice to make neutrino masses positive.

Phantom dark energy at high redshift is a key characteristic.

Crossing w=-1 at lower redshift is necessary.

Abstract

A puzzling implication of current data interpreted in the $\Lambda$CDM cosmology is the preference for a negative sum of neutrino masses. Moving to $w_0w_a$CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case $w$CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing $w=-1$ at lower redshift.