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

Abstract

Template banks containing gravitational wave (GW) waveforms are essential for matched-filtering GW search pipelines. We describe the generation method, the design, and validation of the template bank used by the GstLAL-based inspiral pipeline to analyze data from the fourth observing run of LIGO scientific, Virgo, and KAGRA collaboration. This paper presents a template bank containing $1.8 \times 10^6$ templates that include merging neutron star - neutron star, neutron star - black hole, and black hole - black hole systems up to a total mass of $400$ $M_\odot$. Motivated by observations, component masses below $3$ $M_\odot$ have dimensionless spins ranging between $\pm 0.05$, while component masses between $3$ to $200$ $M_\odot$ have dimensionless spins ranging between $\pm 0.99$, where we assume spin-aligned systems. The low-frequency cutoff is $15$ Hz. The templates are placed in the parameter space according to the metric via a binary tree approach which took $\mathcal{O}\left(10\right)$ minutes when jobs were parallelized. The template bank generated with this method has a $98\%$ match or higher for $90\%$ of the injections, thus being as effective as the template placement method used for the previous observation runs. The volumes of the templates are computed prior to template placement and the nearby templates have similar volumes in the coordinate space, henceforth, enabling a more efficient and less biased implementation of population models. SVD sorting of the O4 template bank has been renewed to use post-Newtonian phase terms, which improved the computational efficiency of SVD by nearly $4 \sim 5$ times as compared to conventional SVD sorting schemes. Template banks and searches focusing on the sub-solar mass parameter space and intermediate-mass black hole parameter space are conducted separately