Abstract
Upcoming ground and space-based experiments may have sufficient accuracy to
place significant constraints upon high-redshift star formation, Reionization,
and dark matter (DM) using the global 21-cm signal of the IGM. In the early
universe, when the relative abundance of low-mass DM halos is important,
measuring the global signal would place constraints on the damping of structure
formation caused by DM having a higher relic velocity (warm dark matter, or
WDM) than in cold dark matter (CDM). Such damping, however, can be mimicked by
altering the star formation efficiency (SFE) and difficult to detect because of
the presence of Pop III stars with unknown properties. We study these various
cases and their degeneracies with the WDM mass parameter $m_X$ using a Fisher
matrix analysis. We study the $m_X = 7$ keV case and a star-formation model
that parametrizes the SFE as a strong function of halo mass and include several
variations of this model along with three different input noise levels for the
likelihood. We find that when the likelihood includes only Pop II stars, $m_X$
is constrained to $0.4$ keV for all models and noise levels at 68$\%$ CI.
When the likelihood includes weak Pop III stars, $m_X 0.3$ keV, and if Pop
III star formation is relatively efficient, $m_X 0.1$ keV, with tight Pop
III star-formation parameter constraints. Our results show that the global
21-cm signal is a promising test-bed for WDM models, even in the presence of
strong degeneracies with astrophysical parameters.
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