Search for precessing binary black holes in advanced LIGO’s third observing run using harmonic decomposition

Binary black holes (BBHs) exhibiting spin-induced orbital precession offer unique insight into compact-binary formation channels, cosmology, and tests of general relativity. We conduct a dedicated search for precessing BBHs with unequal masses in Advanced LIGO’s third observing run (O3) using the harmonic decomposition method of precessing waveforms. We introduce a novel scheme to reduce the number of filters in a harmonic search. With our new approach, our template bank requires 5 × fewer filters compared to another proposed precessing search in the same region. We do not find any new significant events. Our new search method achieves up to ∼28% improvement in sensitivity and up to 5 × lower computational costs compared to existing precessing search pipelines. Our method enables scalable, sensitive searches for precessing BBHs in future gravitational-wave observing runs.