Cosmological Constraints on Neutrino Masses in a Second-Order CPL Dark Energy Model

TL;DR

This study compares how different dark energy models and datasets influence the upper limits on neutrino masses, finding that the choice of model and data significantly impacts the constraints, with no evidence for nonzero neutrino mass beyond oscillation limits.

Contribution

It introduces and analyzes a second-order correction to the CPL dark energy parameterization and compares neutrino mass bounds across multiple models and datasets using Bayesian and frequentist methods.

Findings

CPL yields tighter neutrino mass bounds than EXP.

Neutrino mass constraints are only mildly sensitive to hierarchy assumptions.

Frequentist bounds are generally tighter than Bayesian bounds.

Abstract

Recent DESI results indicate a strong preference for dynamical dark energy (DE) when baryon acoustic oscillation (BAO) measurements are combined with supernovae (SNe) and cosmic microwave background (CMB) data using the Chevallier-Polarski-Linder (CPL) parameterization. We analyze the exponential (EXP) parameterization, which introduces a second-order correction to CPL. We determine and compare the 95% upper bounds on the sum of neutrino masses for three dark energy (DE) models -- $\Lambda$CDM, CPL, and EXP -- across four neutrino mass hierarchies (1 massive/2 massless, degenerate, normal, inverted) and multiple dataset combinations (CMB$+$BAO, CMB$+$BAO$+$PantheonPlus, CMB$+$BAO$+$DESY5), employing both Bayesian and frequentist frameworks with physical lower limits from oscillation experiments (0.059 eV and 0.11 eV). Our results show that CPL yields tighter ($\lesssim10$%) bounds compared to EXP. We further confirm earlier findings that neutrino mass constraints are only mildly sensitive to the assumed hierarchy and that the frequentist bounds are tighter than Bayesian ones. Furthermore, the imposed oscillation lower limits, the datasets used and the DE parameterizations play a crucial role in the inferred cosmological neutrino mass bounds. For the datasets, hierarchies, and DE parameterizations considered, we find no statistically significant evidence for nonzero neutrino mass consistent with oscillation lower limits.