Constraints on the Primordial Black Hole Abundance using Pulsar Parameter Drifts

TL;DR

This paper uses pulsar parameter drifts to set upper limits on primordial black hole abundance, challenging their role in explaining LIGO-Virgo-KAGRA black hole observations.

Contribution

First search for scalar-induced gravitational waves via pulsar drifts, providing new constraints on primordial black holes across a broad mass range.

Findings

Placed a 95% confidence upper limit of $f_{PBH} < 10^{-10}$ on PBH abundance.

Strongly disfavor PBHs as the origin of current LIGO-Virgo-KAGRA black hole detections.

Demonstrated pulsar parameter drifts as a novel probe for early Universe phenomena.

Abstract

Primordial black holes (PBHs) provide a compelling interpretation for the binary black holes (BBHs) observed by ground-based gravitational-wave (GW) detectors, especially for those BBHs in the theoretical mass gap. In the early Universe, the scalar perturbations required to produce such PBHs inevitably generate scalar-induced GWs (SIGWs). These SIGWs peak in the sub-nanohertz band, and manifest secularly as measurable jerk-like drifts in the second derivative of pulsar spin periods. In this Letter, we perform the first search for SIGWs using pulsar parameter drifts, and place a 95\% confidence-level upper limit on the PBH abundance of $f_{\mathrm{PBH}} < 10^{-10}$ over the mass range $[3 \times 10^{-1}, 4 \times 10^{4}] M_{\odot}$. Our results strongly disfavor a PBH origin for the BBHs currently detected by the LIGO-Virgo-KAGRA (LVK) Collaborations.