Constraints on primordial black holes.

We update the constraints on the fraction of the Universe that may have gone into primordial black holes (PBHs) over the mass range 10to 10 g. Those smaller than ∼10 g would have evaporated by now due to Hawking radiation, so their abundance at formation is constrained by the effects of evaporated particles on big bang nucleosynthesis, the cosmic microwave background (CMB), the Galactic and extragalactic-ray and cosmic ray backgrounds and the possible generation of stable Planck mass relics. PBHs larger than ∼10 g are subject to a variety of constraints associated with gravitational lensing, dynamical effects, influence on large-scale structure, accretion and gravitational waves.