Clustering of primordial black holes: Basic results

We investigate the spatial clustering properties of primordial black holes (PBHs). With minimal assumptions, we show that PBHs created in the radiation era are highly clustered. Using the peaks theory model of bias, we compute the PBH two-point correlation function and power spectrum. For creation from an initially adiabatic power spectrum of perturbations, the PBH power spectrum contains both isocurvature and adiabatic components. The absence of observed isocurvature fluctuations today constrains the mass range in which PBHs may serve as dark matter. We briefly discuss other consequences of PBH clustering.