Template bank for subsolar mass compact binary mergers in the fourth observing run of Advanced LIGO, Advanced Virgo, and KAGRA

Matched-filtering searches for gravitational-wave signals from compact binary mergers employ template banks which are a collection of modeled waveforms described by unique intrinsic parameters. We present two banks designed for low-latency and archive subsolar mass (SSM) searches in data from the fourth observing run of LIGO-Virgo-KAGRA, and demonstrate the efficacy of the banks via simulated signals. Further, we introduce several new methodological developments to the geometric placement algorithm [C. Hanna et al., Phys. Rev. D 108, 042003 (2023); C. Hanna, MANIFOLD (2024)], including a more stable metric-estimation technique and a boundary-padding procedure. Together, these enhancements enable the method to work for exceedingly low component masses necessary for SSM bank production, representing the first successful application of the MANIFOLD-method to lower-mass regions of the compact binary parameter space. The archive search bank contains a total of 3,452,006 templates, and covers a mass parameter space of 0.2 to 10M⊙ in the larger component and 0.2 to 1.0M⊙ in the smaller component, the spin parameter space of −0.9 to 0.9 for masses above 0.5M⊙ and −0.1 to 0.1 for masses below 0.5M⊙, and the mass ratio parameter space of 1 to 10. The power spectral density used was from a week of the first half of the fourth observing run of Advanced LIGO, Advanced Virgo, and KAGRA, and the low frequency cutoff was set to 45 Hz with a maximum waveform duration of 128 secs. The bank simulations performed using SBank have shown that the banks presented in this paper have sufficient efficacy for use in their respective searches.