First higher-multipole model of gravitational waves from spinning and coalescing black-hole binaries

TL;DR

This paper introduces PhenomHM, the first higher-multipole gravitational wave model for spinning black-hole binaries, improving accuracy and parameter estimation over dominant-multipole models by incorporating subdominant multipoles without additional numerical relativity tuning.

Contribution

It presents a simple, non-tuning method to include subdominant multipoles in gravitational waveforms, resulting in the first higher-multipole model for spinning black-hole binaries.

Findings

PhenomHM outperforms dominant-multipole models in accuracy across all configurations.

Inclusion of higher multipoles improves binary property measurements.

The method requires no additional numerical relativity tuning.

Abstract

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.