Probing primordial black hole mergers in clusters with pulsar timing data
Phys. Rev. D 114, 083532 – Published 20 October, 2026
DOI: https://doi.org/10.1103/j38g-ft2h
Abstract
We consider the possibility that the stochastic gravitational wave (GW) background suggested by pulsar timing array (PTA) datasets is sourced by primordial black holes (PBHs). Specifically, we perform a Bayesian search in the International PTA data release 2 (IPTA DR2) for a combined GW background arising from scalar perturbations and unresolved PBH mergers, assuming a broad PBH mass distribution. In our analysis, we incorporate constraints on the curvature power spectrum from cosmic microwave background distortions and the overproduction of PBHs, which significantly suppress the contribution of PBH mergers to the total GW background. We find that scalar-induced GWs dominate the nanohertz frequency range, while PBH mergers alone cannot account for the observed signal under the standard PBH formation scenario involving Gaussian perturbations and including only Poissonian PBH clustering. However, specific PBH models, such as those with enhanced clustering, could yield a GW background dominated by PBH mergers. Overall, we find that the IPTA DR2 strongly favors an astrophysical origin for the reported common-spectrum process over the PBH models considered in this analysis.
