Numerical-relativity validation of effective-one-body waveforms in the intermediate-mass-ratio regime

One of the open problems in developing binary black hole (BBH) waveforms for gravitational wave astronomy is to model the intermediate mass ratio regime and connect it to the extreme mass ratio regime. A natural approach is to employ the effective one body (EOB) approach to the two-body dynamics that, by design, can cover the entire mass ratio range and naturally incorporates the extreme mass ratio limit. Here we use recently obtained numerical relativity (NR) data with mass ratios $m_1/m_2=(7,15,\,32,\,64,\,128)$ to test the accuracy of the state-of-the-art EOB model TEOBResumS in the intermediate mass ratio regime. We generally find an excellent EOB/NR consistency around merger and ringdown for all mass ratios and for all available subdominant multipoles, except for the $\ell=m=5$ one. This mode can be crucially improved using the new large-mass ratio NR data of this paper. The EOB/NR inspirals are also consistent with the estimated NR uncertainties. We also use several NR datasets taken by different public catalogs to probe the universal behavior of the multipolar hierarchy of waveform amplitudes at merger, that smoothly connects the equal-mass BBH to the test-mass result. Interestingly, the universal behavior is strengthened if the nonoscillatory memory contribution is included in the NR waveform. Future NR simulations with improved accuracy will be necessary to further probe, and possibly quantitatively refine, the TEOBResumS transition from late inspiral to plunge in the intermediate mass ratio regime.