On the merger rate of primordial black holes: effects of nearest neighbours distribution and clustering
Abstract
One of the seemingly strongest constraints on the fraction of dark matter in the form of primordial black holes (PBH) of Script O(10) M_{solar} relies on the merger rate inferred from the binary BH merger events detected by LIGO/Virgo. The robustness of these bounds depends however on the accuracy with which the formation of PBH binaries in the early Universe can be described. We revisit the standard estimate of the merger rate, focusing on a couple of key ingredients: the spatial distribution of nearest neighbours and the initial clustering of PBHs associated to a given primordial power spectrum. Overall, we confirm the robustness of the results presented in the literature in the case of a narrow mass function (which constrain the PBH fraction of dark matter to be f_{PBH}lesssim 0.0010.01). The initial clustering of PBHs might have an effect tightening the current constraint, but only for very broad mass functions, corresponding to wide bumps in the primordial power spectra extending at least over a couple of decades in kspace.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 October 2018
 DOI:
 10.1088/14757516/2018/10/043
 arXiv:
 arXiv:1807.02084
 Bibcode:
 2018JCAP...10..043B
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Phenomenology
 EPrint:
 Extended computations and results reported in Sec. 4, clarifications added (notably in Sec. 4 and 5), several typos corrected. Results unchanged. Matches version to appear in JCAP