Implications for PBH Dark Matter from a single Sub-Solar$\unicode{x2013}$GW Detection in LVK O1$\unicode{x2013}$O4

Abstract: The detection of sub-solar mass black holes is a milestone of modern astrophysics as it would open a window either onto new stellar physics or could potentially unveil the nature of Dark Matter as Primordial Black Holes. On November 12, 2025, the LIGO-Virgo-KAGRA (LVK) collaboration reported the compact binary merger candidate S251112cm, a system with no obvious EM counterpart, consistent with binary black hole merger with a chirp mass in the range $0.1-0.87 \, M_\odot$. The probability that at least one component has mass $<$1 $M_{\odot}$ is $>99\%$. Inspired by this trigger, we tested if a population of PBHs formed at Quantum Chromodynamics epoch with a broad mass function could account for a signal of this type. Our results, corresponding to a predicted event rate of $0.8 \,\text{yr}^{-1}$ as seen by LVK O3b, suggest that the observed merger rate of $0.23^{+0.86}_{-0.218}\,\text{yr}^{-1}\;(95\%\;\text{C.L.})$ if the trigger is confirmed as an astrophysical event would be compatible with such a model. Our predicted detection rate is also in agreement with current LVK expectations for stellar-mass binaries, remaining consistent with a scenario in which a non-negligible fraction of the $3-200 \;M_\odot$ mergers observed by LVK originate from Primordial Black Holes. If confirmed, this detection would place a lower limit to the PBH abundance $f_{PBH}>0.04$ for our adopted model.