Constraining the Initial Primordial Black Hole Clustering with CMB-distortion

TL;DR

This paper investigates how local primordial non-Gaussianity could induce initial clustering of primordial black holes and how future CMB $d$-distortion measurements can test this hypothesis, with current limits already constraining the non-Gaussianity level.

Contribution

It demonstrates that future CMB $d$-distortion experiments can probe primordial black hole clustering caused by local non-Gaussianity, linking early universe conditions to observable signatures.

Findings

Future CMB $d$-distortion experiments can test primordial black hole clustering hypotheses.

Existing limits imply that significant local non-Gaussianity is required for clustering.

Primordial black holes are initially Poisson-distributed absent non-Gaussianity.

Abstract

The merger rate of primordial black holes depends on their initial clustering. In the absence of primordial non-Gaussianity correlating short and large-scales, primordial black holes are distributed \`a la Poisson at the time of their formation. However, primordial non-Gaussianity of the local-type may correlate primordial black holes on large-scales. We show that future experiments looking for CMB $\mu$-distortion would test the hypothesis of initial primordial black hole clustering induced by local non-Gaussianity, while existing limits already show that significant non-Gaussianity is necessary to induce primordial black hole clustering.