Constraining the neutrino mass using a multi-tracer combination of two galaxy surveys and CMB lensing

TL;DR

This paper explores how combining 21cm intensity mapping, galaxy surveys, and CMB data can significantly improve constraints on the total neutrino mass, leveraging multi-tracer techniques to reduce cosmic variance.

Contribution

It demonstrates that a multi-tracer approach with upcoming surveys can tighten neutrino mass constraints to below 50 meV without relying on priors.

Findings

Multi-tracer combination reduces neutrino mass uncertainty to ~45 meV.

Adding LSST clustering data further improves the constraint to ~12 meV.

Using linear clustering information without priors is sufficient for strong constraints.

Abstract

Measuring the total neutrino mass is one of the most exciting opportunities available with next-generation cosmological data sets. We study the possibility of detecting the total neutrino mass using large-scale clustering in 21cm intensity mapping and photometric galaxy surveys, together with CMB information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multi-tracer analysis in order to reduce cosmic variance. The multi-tracer combination of an SKAO-MID 21cm intensity map with Stage~4 CMB dramatically shrinks the uncertainty on total neutrino mass to $\sigma(M_\nu) \simeq 45\,$meV, using only linear clustering information ($k_{\rm max} = 0.1\, h/$Mpc) and without a prior on optical depth. When we add to the multi-tracer the clustering information expected from LSST, the forecast is $\sigma(M_\nu) \simeq 12\,$meV.