Speaker
Description
Primordial black holes (PBHs) are compelling candidates for dark matter (DM), although current observations strongly limit their ability to account for the total DM abundance. In scenarios where the remaining DM consists of weakly interacting massive particles (WIMPs), the latter are expected to accumulate around PBHs, forming dense dark matter spikes whose properties can be predicted rather accurately. These spikes can significantly enhance the overall WIMP annihilation rate. Using observations of the isotropic $\gamma$-ray background and point-like sources in the Galactic halo, we derive new constraints on this scenario, which differ from (and are more reliable than) past extrapolations of limits on decaying dark matter. Assuming standard WIMP properties, the DM fraction in the form of PBHs is constrained to $f_\mathrm{BH} < 10^{-8}$, even for asteroid-mass PBHs. Conversely, the observation of sub-solar mass PBHs like those hinted by recent analyses of the HSC data would imply extremely strong limits on the s-wave annihilation cross section. These results highlight the strong complementarity between PBH searches and indirect detection of particle dark matter.
