  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 intergalactic medium.
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 also use a minimum halo virial
temperature for collapse near the molecular cooling threshold. We find that
when the likelihood includes only Pop II stars, $m_X$ is constrained to an
uncertainty of $\sim 0.4$ keV for all models and noise levels at 68$\%$ CI.
When the likelihood includes weak Pop III stars, $m_X \sim 0.3$ keV, and if Pop
III star formation is relatively efficient, $m_X \sim 0.1$ keV uncertainty,
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.

Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies