Boosting small-scale structure via primordial black holes and
  implications for sub-GeV dark matter annihilation
  We explore the possibility that the annihilation of dark matter (DM) is
boosted due to enhanced substructure in the presence of primordial black holes
(PBHs) which constitute a sub-component of DM. The PBHs can generate entropy
fluctuations at the small scales which trigger early structure formation, and a
large fraction of the whole DM can reside in these collapsed objects that
formed at high redshift ($z\gtrsim 100$). Such early forming minihalos
consequently possess higher densities than those in the conventional scenarios
(without PBHs) and would be more resilient to tidal disruptions. Our scenarios
of the annihilation boost due to DM substructures are of particular interest
for light ($< 1$ GeV) DM which has been less explored compared to heavier DM in
the presence of the PBHs.
