Search for CBCs with SSM Components in Data from The First Part of LVK Fourth Observing Run

Abstract

Star evolution models predict the lightest compact objects in the universe to have masses greater than that of the Sun. Nonetheless, alternative scenarios could lead to the formation of sub-solar mass (SSM) compact objects, such as primordial black holes (PBHs). The LIGO-Virgo-KAGRA Collaboration (LVK) has performed a search for gravitational-wave (GW) signals from compact binary coalescences (CBCs) including at least one SSM component during the first part of their fourth observing run (O4a), reporting no statistically significant candidate. This non-detection sets upper limits on the merger rate of such systems, which can be used to constrain PBH formation models and the fraction of dark matter (DM) in PBHs. For PBH binaries forming at late times, the fraction of DM in PBHs is constrained to be <= 1 for masses above 0.9 M_sun in the case of monochromatic mass functions. In the early-formation scenario, this fraction is limited to $\le 7\%$ at 1 $M_\odot$ and $\le 40\%$ at 0.35 $M_\odot$.