Higher order gravitational-wave modes with likelihood reweighting

The leading order gravitational emission from binary black hole mergers is well described by just the quadrupolar emission. However, to fully characterise the waveform it is necessary to include additional “higher-order” modes. Including these higher-order contributions in the waveform leads to a large increase in computational cost which make them difficult to use for parameter estimation. In this work, we propose using “likelihood reweighting”, a form of importance sampling, to perform initial parameter estimation with a quadrupole only waveform, and then weighting each of the posterior samples to generate a posterior including the effect of higher-order modes.