Abstract
Fuzzy dark matter (FDM) is a well motivated candidate for dark matter (DM) as
its tiny mass and large de-Broglie wavelength suppress small-scale matter
fluctuations, thereby solving some of the small-scale discrepancies in
$Łambda$CDM. Although it has been ruled out as the single component of DM by
several observables, there is still a region in the FDM parameter space (the
"FDM window", $10^-25\,eVłesssim
m_FDMłesssim10^-23\,eV$) where FDM is allowed to comprise
a large portion of the total DM. In this work, for the first time, we study the
signature of FDM (comprised of ultra-light axions) in fractions less than unity
on the 21cm signal and its detectability by 21cm interferometers such as HERA,
taking into account the degeneracy with both astrophysical and cosmological
parameters, using a new pipeline that combines modified versions of the CAMB
and 21cmFAST codes. Our forecasts imply that HERA in its design performance
will be sensitive to FDM fractions as small as 1% in the FDM window, and
improve over existing bounds for other masses by up to an order of magnitude.
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