Testing general relativity using higher-order modes of gravitational waves from binary black holes

Recently, strong evidence was found for the presence of higher-order modes in the gravitational wave signals GW190412 and GW190814, which originated from compact binary coalescences with significantly asymmetric component masses. This has opened up the possibility of new tests of general relativity by looking at the way in which the higher-order modes are related to the basic signal. Here we further develop a test which assesses whether the amplitudes of subdominant harmonics are consistent with what is predicted by general relativity. To this end we incorporate a state-of-the-art waveform model with higher-order modes and precessing spins into a Bayesian parameter estimation and model selection framework. The analysis methodology is tested extensively through simulations. We investigate to what extent deviations in the relative amplitudes of the harmonics will he measurable depending on the properties of the source, and we map out correlations between our testing parameters and the inclination of the source with respect to the observer. Finally, we apply the test to GW190412 and GW190814, finding no evidence for violations of general relativity.

Automated summary

Evidence for higher-order modes in gravitational wave signals has been found, allowing for new tests of general relativity. A test was developed to assess the consistency of the amplitudes of subdominant harmonics with general relativity predictions. Through simulations, the researchers investigated the extent to which deviations in harmonic amplitudes can be measured depending on source properties, and identified correlations between testing parameters and the inclination of the source relative to the observer. Finally, the test was applied to actual gravitational wave data, finding no violations of general relativity.