Hawking radiation from primordial black holes (PBH) can ionize and heat up neutral gas during the cosmic dark ages, leaving imprints on the global 21-cm signal of neutral hydrogen. We use the global 21-cm signal to constrain the abundance of spinning PBHs in mass range of $[2 \times 10^{ 13}, 10^{ 18}]$ grams. We consider several extended PBH distribution models. Our results show that 21-cm can set the most stringent PBH bounds in our mass window. Compared with constraints set by { \it 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 21-cm constraints for the monochromatic mass distribution rule out spinless PBHs with initial mass below $1.5 \times 10^{ 17}\ \r{ g}$, whereas extreme Kerr PBHs with reduced initial spin of $a_0=0.999$ are excluded as the dominant dark matter component for masses below $6 \times 10^{ 17}\ \r{ g}$. We also derived limits for the log-normal, power-law and critical collapse PBH mass distributions.
Categories: astro-ph.CO hep-ph