Towards a cosmological neutrino mass detection

TL;DR

Future cosmological observations, especially CMB lensing and BAO, are promising for detecting the total neutrino mass with high precision, potentially reaching a 4σ significance for the minimal mass over the next decade.

Contribution

This paper provides forecasts for neutrino mass detection using upcoming cosmological measurements, analyzing how different experiments and model extensions affect the precision.

Findings

Projected neutrino mass uncertainty can reach 15 meV with next-generation experiments.

Current uncertainties (~103 meV) will improve significantly with upcoming CMB and BAO surveys.

Including curvature and dark energy parameters increases the forecasted mass error, highlighting the need for complementary probes.

Abstract

Future cosmological measurements should enable the sum of neutrino masses to be determined indirectly through their effects on the expansion rate of the Universe and the clustering of matter. We consider prospects for the gravitationally lensed Cosmic Microwave Background anisotropies and Baryon Acoustic Oscillations in the galaxy distribution, examining how the projected uncertainty of $\approx15$ meV on the neutrino mass sum (a 4$\sigma$ detection of the minimal mass) might be reached over the next decade. The current 1$\sigma$ uncertainty of $\approx 103$ meV (Planck-2015+BAO-15) will be improved by upcoming 'Stage-3' CMB experiments (S3+BAO-15: 44 meV), then upcoming BAO measurements (S3+DESI: 22 meV), and planned next-generation 'Stage 4' CMB experiments (S4+DESI: 15-19 meV, depending on angular range). An improved optical depth measurement is important: the projected neutrino mass uncertainty increases to $26$ meV if S4 is limited to $\ell>20$ and combined with current large-scale polarization data. Looking beyond $\Lambda$CDM, including curvature uncertainty increases the forecast mass error by $\approx$ 50% for S4+DESI, and more than doubles the error with a two-parameter dark energy equation of state. Complementary low-redshift probes including galaxy lensing will play a role in distinguishing between massive neutrinos and a departure from a $w=-1$, flat geometry.