Time- and frequency-domain waveform models for the gravitational-wave memory effect

After the passage of a gravitational-wave (GW) signal, a permanent relative displacement between two freely falling test masses generically occurs, which is called the GW memory effect. Searches for the memory effect in GW detector data require accurate waveform models, which must be evaluated many times (and, thus, need to be evaluated rapidly). Current analytical waveform models and many numerical-relativity waveforms and surrogates of binary-black-hole (BBH) mergers do not include the memory effect. Instead, GW memory is computed from waveforms without memory by using conservation laws in asymptotically flat spacetimes, which is relatively slow. We therefore develop time- and frequency-domain waveform models of the GW memory effect for nonspinning BBH mergers for comparable-mass systems. We also develop a fit for the final memory offset that incorporates data from both comparable and extreme mass-ratio limits. In addition to speeding up GW searches, having these analytic models will give analytical insight into the time- and frequency-domain properties of the GW memory signal.