Searches for Binary Mergers with Sub-solar Mass Components in Data from the First Part of LIGO--Virgo--KAGRA's Fourth Observing Run

TL;DR

This paper reports a search for sub-solar mass compact binary mergers using LIGO-Virgo-KAGRA data, finding no candidates but setting upper limits that constrain dark matter models involving primordial black holes and dark black holes.

Contribution

First search to set upper limits on sub-solar mass black hole mergers and constrain related dark matter scenarios using recent gravitational wave data.

Findings

No sub-solar mass merger candidates detected.

Upper limits on merger rates range from 110 to 10,000 Gpc^{-3}yr^{-1}.

Constraints exclude certain primordial black hole dark matter fractions.

Abstract

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 also reporting the sensitivity of the search to low-mass neutron star binaries for the first time. With the absence of detections, we place upper limits on the merger rate of sub-solar mass black holes, ranging from $110$ $\mathrm{Gpc^{-3}yr^{-1}}$ to $10000$ $\mathrm{Gpc^{-3}yr^{-1}}$ at 90% confidence. 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 late-forming primordial black hole binaries, our search excludes the fraction of dark matter in primordial black holes to be 1 for masses above $0.9 M_\odot$. 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) $\times10^{-5}$ when the minimum mass is $1 M_\odot$. For binary neutron stars that include sub-solar mass components, we estimate the sensitive space-time hypervolume to be $10^{-3}$ $\mathrm{Gpc^3yr}$, and report the upper limit on their merger rate for a simple, fixed population as ~86 $\mathrm{Gpc^{-3}yr^{-1}}$.