Gravitational-wave observations of binary black holes currently rely on theoretical models that predict the dominant multipoles (l,m) of the radiation during inspiral, merger and ringdown. We introduce a simple method to include the subdominant multipoles to binary black hole gravitational waveforms, given a frequency-domain model for the dominant multipoles. The amplitude and phase of the original model are appropriately stretched and rescaled using post-Newtonian results (for the inspiral), perturbation theory (for the ringdown), and a smooth transition between the two. No additional tuning to numerical-relativity simulations is required. We apply a variant of this method to the non-precessing PhenomD model. The result, PhenomHM, constitutes the first higher-multipole model of spinning black-hole binaries, and currently includes the (l,m) = (2,2), (3,3), (4,4), (2,1), (3,2), (4,3) radiative moments. Comparisons with numerical-relativity waveforms demonstrate that PhenomHM is more accurate than dominant-multipole-only models for all binary configurations, and typically improves the measurement of binary properties.
@article{arxiv.1708.00404,
title = {First higher-multipole model of gravitational waves from spinning and coalescing black-hole binaries},
author = {Lionel London and Sebastian Khan and Edward Fauchon-Jones and Cecilio García and Mark Hannam and Sascha Husa and Xisco Jiménez Forteza and Chinmay Kalaghatgi and Frank Ohme and Francesco Pannarale},
journal= {arXiv preprint arXiv:1708.00404},
year = {2018}
}