EVOLUTION OF A PRIMORDIAL BLACK-HOLE POPULATION - ART. NO. 023504

We reconsider in this work the effects of an energy absorption term in the evolution of primordial black holes (PBHs) in several epochs of t he Universe. A critical mass is introduced as a boundary between the a ccreting and evaporating regimes of the PBHs. We show that the growth of PBHs is negligible in the radiation-dominated era due to the scarci ty of the energy density supply from the expanding background, in agre ement with a previous analysis by Carr and Hawking, but that neverthel ess the absorption term is large enough for black holes above the crit ical mass to preclude their evaporation until the universe has cooled sufficiently. The effects of PBH motion are also discussed: the Dopple r effect may increase the energy accretion in black holes with large p eculiar motions relative to background. We discuss how cosmological co nstraints are modified by the introduction of the critical mass since PBHs above it do not disturb the cosmic microwave background radiation . We show that there is a large range of admissible masses for PBHs ab ove the critical mass, but well below the cosmological horizon. Finall y we outline a minimal kinetic formalism, solved in some limiting case s, to deal with more complicated cases of PBH populations. [S0556-2821 (98)00414-7].