LIGO Document P2400387-v10
- We report on a gravitational wave search for compact binary coalescences involving at least one component with mass between 0.2 \( M_\odot \) to 1 \( M_\odot \), and ratio of component masses between 0.1 and 1. The analysis uses data collected by the LIGO detectors between May 24 2023 15:00 UTC and January 16 2024 16:00 UTC. No statistically significant sub-solar mass candidates were identified by the participating search algorithms. We report the detection sensitivity of the current searches to the target sub-solar mass black hole population, while extending the scope of previous searches to consider low-mass neutron star binaries. With the absence of detections, we place upper limits on the merger rate of sub-solar mass black holes, ranging from \( 110 \,\mathrm{Gpc}^{-3} \,\mathrm{yr}^{-1} \) to \( 10000 \,\mathrm{Gpc}^{-3} \,\mathrm{yr}^{-1} \) at 90% confidence. For binary neutron stars that include sub-solar mass components, we estimate the sensitive space-time hypervolume to be \( \sim 10^{-3} \,\mathrm{Gpc}^3 \,\mathrm{yr} \), and report the upper limit on their merger rate for a simple, fixed population as \( \sim 86 \,\mathrm{Gpc}^{-3} \,\mathrm{yr}^{-1} \). We use the merger rate limits to constrain two illustrative dark matter scenarios that can form sub-solar mass compact objects: primordial black holes, and dark black holes forming in a dissipative dark matter model. For primordial black hole binaries forming at late times, the fraction of dark matter in primordial black holes \( \leq \) 1 for masses above 0.9 \( M_\odot \) for monochromatic mass functions. In the early-formation scenario, we limit this fraction to be \( \leq \) 7% at 1 \( M_\odot \), and \( \leq \) 40% at 0.35 \( M_\odot \). For the dissipative model, the excluded region in the parameter space of dark matter fraction in dark black holes and their minimum possible mass extends down to (1.2 to 1.3) \( \times 10^{-5} \) when the minimum mass is 1 \( M_\odot \).
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