Numerical simulations of low-mass black hole-neutron star mergers with moderate eccentricities

A confident detection of orbital eccentricity in gravitational-wave signals from black hole-neutron star systems would be a strong indicator of their dynamical formation origin. While eccentric waveform models have recently been developed, their validity for analyzing black hole--neutron star signals has yet to be tested against numerical-relativity simulations. Building upon our previous study of quasicircular black hole--neutron star mergers, we perform simulations of a subset of these systems with orbital eccentricities around five times larger than those inferred for GW200105 162426. Additionally, we perform simulations with magnetized matter to assess whether trapped g-mode oscillations persist in strongly magnetized disks. Regarding the emitted gravitational-wave signal, we find that the effective one-body waveform model SEOBNRv5EHM shows reasonable agreement unless tidal contributions become important, and the inspiral-only post-Newtonian models pyEFPE/pyEFPEHM show larger disagreement in the late inspiral. For the equal-mass system, which has the largest effective tidal deformability, eccentric tidal corrections have a small but noticeable impact on the phase, about0.1 rad. We find an almost negligible impact of eccentricity on the properties of the remnant black hole, and differences of up to a factor of two in the remnant disk mass. Trapped g modes in the accretion disks have the same frequency regardless of the eccentricity, confirming that they depend mainly on the properties of the remnant black hole. We find that when accretion disks are strongly magnetized, they become less dense and have less pronounced structure, and that the trapped g modes previously identified in the unmagnetized cases are efficiently damped.