We focus on the ongoing and future observations for both the 21 cm line and the CMB B-mode polarization produced by a CMB lensing, and study their sensitivities to the effective number of neutrino species, the total neutrino mass, and the neutrino mass hierarchy. We find that combining the CMB observations with future square kilometer arrays optimized for 21 cm line such as Omniscope can determine the neutrino mass hierarchy at 2σ. We also show that a more feasible combination of Planck+Polarbear and SKA can strongly improve errors of the bounds on the total neutrino mass and the effective number of neutrino species to be δσm ν ~0.12 eV and δN ν ~0.38 at 2σ, respectively. © 2012 Elsevier B.V.
Oyama, Y., Shimizu, A., & Kohri, K. (2013). Determination of neutrino mass hierarchy by 21 cm line and CMB B-mode polarization observations. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 718(4–5), 1186–1193. https://doi.org/10.1016/j.physletb.2012.12.053