Toward numerical-relativity informed effective-one-body waveforms for dynamical capture black hole binaries

Dynamical captures of black holes may take place in dense stellar media due to the emission of gravitational radiation during a close passage. Detection of such events requires detailed modeling, since their phenomenology qualitatively differs from that of quasicircular binaries. Very few models can deliver such waveforms, and none includes information from numerical relativity (NR) simulations of nonquasicircular coalescences. In this study we present a first step towards a fully NR-informed effective-one-body (EOB) model of dynamical captures. We perform 14 new simulations of single and double encounter mergers, and use this data to inform the merger-ringdown model of the TEOBResumS-Dalì approximant. We keep the initial energy approximately fixed to the binary mass, and vary the mass-rescaled, dimensionless angular momentum in the range (0.6, 1.1), the mass ratio in (1, 2.15), and aligned dimensionless spins in (-0.5,0.5). We find that the model is able to match NR to 97%, improving previous performances, without the need of modifying the baseline template. Upon NR informing the model, this improves to 99% with the exception of one outlier corresponding to a direct plunge. The maximum EOB/NR phase difference at merger for the uninformed model is of 0.15 radians, which is reduced to 0.1 radians after the NR information is introduced. We outline the steps towards a fully informed EOB model of dynamical captures, and discuss future improvements.