Constraints on the neutrino parameters by future cosmological 21cm line
  and precise CMB polarization observations
  Observations of the 21 cm line radiation coming from the epoch of
reionization have a great capacity to study the cosmological growth of the
Universe. Also, CMB polarization produced by gravitational lensing has a large
amount of information about the growth of matter fluctuations at late time. In
this paper, we investigate their sensitivities to the impact of neutrino
property on the growth of density fluctuations, such as the total neutrino
mass, the effective number of neutrino species (extra radiation), and the
neutrino mass hierarchy. We will show that by combining a precise CMB
polarization observations such as Simons Array with a 21 cm line observation
such as Square kilometer Array (SKA) phase 1 and a baryon acoustic oscillation
observation (Dark Energy Spectroscopic Instrument:DESI) we can measure effects
of non-zero neutrino mass on the growth of density fluctuation if the total
neutrino mass is larger than 0.1eV. Additionally, the combinations can strongly
improve errors of the bounds on the effective number of neutrino species
sigma(N_nu) ~ 0.06-0.09 at 95 % C.L.. Finally, by using SKA phase 2, we can
determine the neutrino mass hierarchy at 95 % C.L. if the total neutrino mass
is similar to or smaller than 0.1 eV.
