Abstract
Hawking radiation from primordial black holes (PBH) can ionize and heat up
neutral gas during the cosmic dark ages, leaving imprints on the global 21cm
signal of neutral hydrogen. We use the global 21cm signal to constrain the
abundance of spinning PBHs in mass range of $2 10^13, 10^18$
grams. We consider several extended PBH distribution models. Our results show
that 21cm can set the most stringent PBH bounds in our mass window. Compared
with constraints set by Planck cosmic microwave background (CMB) data,
21-cm limits are more stringent by about two orders of magnitudes. PBHs with
higher spin are typically more strongly constrained. Our 21cm constraints for
the monochromatic mass distribution rule out spinless PBHs with initial mass
below $1.4 10^17\ g$, whereas extreme Kerr PBHs with reduced
initial spin of $a_0=0.999$ are excluded as the dominant dark matter component
for masses below $6 10^17\ g$. We also derived limits for the
log-normal, power-law and critical collapse distributions.
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