Toward a multitracer neutrino mass measurement with line-intensity mapping

Accurately determining neutrino masses is a main objective of contemporary cosmology. Since massive neutrinos affect structure formation and evolution, probes of large scale structure are sensitive to the sum of their masses. In this work, we explore future constraints on $\ensuremath{\sum}{m}_{\ensuremath{\nu}}$ utilizing line-intensity mapping (LIM) as a promising emerging probe of the density of our Universe, focusing on the fine-structure [CII] line as an example, and compare these constraints with those derived from traditional galaxy surveys. Additionally, we perform a multitracer analysis using velocity tomography via the kinetic Sunyaev-Zeldovich and moving lens effects to reconstruct the three-dimensional velocity field. Our forecasts indicate that the next-generation AtLAST detector by itself can achieve ${\ensuremath{\sigma}}_{\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}}\ensuremath{\sim}50\text{ }\text{ }\mathrm{meV}$ sensitivity. Velocity tomography will further improve these constraints by 4%. Incorporating forecasts for CMB-S4 and DESI-BAO in a comprehensive multitracer analysis, while setting a prior on the optical depth to reionization $\ensuremath{\tau}$ derived using 21-cm forecasted observations, to break degeneracies, we find that a $\ensuremath{\gtrsim}5\ensuremath{\sigma}$ detection of $\ensuremath{\sum}{m}_{\ensuremath{\nu}}\ensuremath{\sim}60\text{ }\text{ }\mathrm{meV}$, under the normal hierarchy, is within reach with LIM. Even without a $\ensuremath{\tau}$ prior, our combined forecast reaches ${\ensuremath{\sigma}}_{\mathrm{\ensuremath{\Sigma}}{m}_{\ensuremath{\nu}}}\ensuremath{\sim}18\text{ }\text{ }\mathrm{meV}$.