Dark matter simulations with primordial black holes in the early Universe

ABSTRACT Primordial black holes (PBH) with masses of order $10\!-\!30 \, \mathrm{M}_\odot$ have been proposed as a possible explanation of the gravitational waves emission events recently discovered by the Laser Interferometer Gravitational-Wave Observatory (LIGO). If true, then PBHs would constitute a sizeable fraction of the dark matter component in the Universe. Using a series of cosmological N-body simulations that include both dark matter and a variable fraction of PBHs ranging from fPBH = 10−4 to fPBH = 1, we analyse the processes of formation and disruption of gravitationally bound PBH pairs, as well as the merging of both bound and unbound pairs, and estimate the probabilities of such events. We show that they are in good agreement with the constrains to the PBH abundance obtained by the LIGO and other research groups. We find that pair stability, while being a main factor responsible for the merger rate, is significantly affected by the effects of dark matter halo formation and clustering. As a side result, we also evaluate the effects of numerical errors in the stability of bound pairs, which can be useful for future research using this methodology.