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
1.8×106 templates that include merging neutron star - neutron star,
neutron star - black hole, and black hole - black hole systems up to a total
mass of 400M⊙​. Motivated by observations, component masses below 3M⊙​ have dimensionless spins ranging between ±0.05, while component
masses between 3 to 200M⊙​ have dimensionless spins ranging between
±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 O(10)
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∼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