Impact of eccentricity and higher modes on neutron star-black hole parameter estimation

Recent detections of gravitational waves from neutron star–black hole (NSBH) systems have opened new avenues for studying extreme matter, constraining formation channels, and probing exotic physics. One such exotic phenomenon — eccentricity, is primarily imprinted on the inspiral phase of a compact binary, which is often limited or missed entirely in binary black-hole observations. NSBH sources produce much longer signals in-band and hence give us ample information to study eccentricity in depth. Limited availability and accuracy of eccentric waveforms in the past have been shown to bias inference of waveform parameters. In this work, we present a systematic parameter-estimation study exploring the impact of eccentricity on parameter inference using injections simulated with the state-of-the-art eccentric waveform model, SEOBNRv5EHM. We find that for the same system, higher eccentricity leads to a reduction in the width of eccentricity posteriors, yielding tighter constraints on correlated parameters. We find no improvement in extrinsic parameters such as distance, sky localization, and polarization angle. However, posterior widths improve noticeably for key intrinsic parameters such as chirp mass and effective spin.