Primordial black holes as dark matter and generators of cosmic structure

Primordial black holes (PBHs) could provide the dark matter but a variety of constraints restrict the possible mass windows to ${10}^{16}-{10}^{17}$g, ${10}^{20}-{10}^{24}$g and $10-{10}^3{M}_{\odot }$. The last possibility is of special interest in view of the recent detection of black-hole mergers by LIGO. PBHs larger than ${10}^3{M}_{\odot }$ might have important cosmological consequences even if they have only a small fraction of the dark matter density. In particular, they could generate cosmological structures either individually through the “seed” effect or collectively through the “Poisson” effect, thereby alleviating some problems associated with the standard cold dark matter scenario.