Constraining light gravitino mass with 21 cm line observation
Abstract
We investigate how well we can constrain the mass of light gravitino m3/2 by using future observations of 21 cm line fluctuations such as Square Kilometre Array (SKA) and Omniscope. Models with light gravitino with the mass m3/2 < O(10) eV are quite interesting because they are free from the cosmological gravitino problem and consistent with many baryogenesis/leptogenesis scenarios. We evaluate expected constraints on the mass of light gravitino from the observations of 21 cm line, and show that the observations are quite useful to prove the mass. If the gravitino mass is m3/2 = 1 eV, we found expected 1 sigma errors on m3/2 are sigma(m3/2) = 0.25 eV (SKA phase 1), 0.16 eV (SKA phase 2) and 0.067 eV (Omniscope) in combination with Planck + Simons Array + DESI (BAO) + H0. Additionally, we also discuss detectability of the effective number of neutrino species by varying the effective number of neutrino species for light gravitino N3/2 and constraints on the mass of light gravitino in the presence of massive neutrinos. We show that 21 cm line observations can detect the nonzero value of N3/2, and allow us to distinguish the effects of the light gravitino from those of massive neutrino.
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