Primordial Black Hole interpretation of the sub-solar merger event S251112cm

Abstract: The LIGO-Virgo-KAGRA (LVK) candidate event S251112cm suggests the presence of at least one compact object with sub-solar masses. Since such objects cannot be produced through standard stellar evolution, this observation provides a potential indication of non-standard formation channels. Primordial black holes (PBHs), formed from the collapse of primordial density fluctuations in the early Universe, are a well-motivated candidate. We investigate the interpretation of S251112cm as the merger of two PBHs with masses in the range 0.1-1$\,M_\odot$. Combining analytic estimates of the PBH merger rate with current observational constraints on their abundance and the sensitivity of LVK searches, we compute the probability of observing such an event. Within a relaxed constraint scenario, the probability reaches unity in the range $M_{\rm PBH} \sim 0.5$-$1\,M_\odot$, while it remains sizable, $\sim \mathcal{O}(0.5)$, in more conservative scenarios and at lower masses. Our results show that a PBH interpretation of S251112cm is viable within current bounds. Owing to the dependence of our results on astrophysical uncertainties, such as those affecting the constraints on the abundance of PBHs, they cannot be regarded as conclusive with respect to the nature of the detected event. At the same time, our analysis highlights the potential of sub-solar gravitational wave events as a probe of PBHs and their contribution to dark matter.