Constraining the neutrino mass using a multitracer combination of two galaxy surveys and cosmic microwave background lensing

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 21 cm intensity mapping and photometric galaxy surveys, together with cosmic microwave background (CMB) information. We include the scale-dependent halo bias contribution due to the presence of massive neutrinos, and use a multitracer analysis in order to reduce cosmic variance. The multitracer combination of an SKAO-MID 21 cm intensity map with stage 4 CMB dramatically shrinks the uncertainty on total neutrino mass to σ(Mν)≃45 meV, using only linear clustering information (⁠kmax=0.1hMpc−1⁠) and without a prior on optical depth. When we add to the multitracer the clustering information expected from Legacy Survey of Space and Time, the forecast is σ(Mν)≃12 meV.