Misinterpreting spin precession as orbital eccentricity in gravitational-wave signals

The increasing scope of gravitational-wave detectors enables the exploration of previously inaccessible parameters in gravitational-wave astronomy. Eccentricity and spin-precession are two key observables that can inform the origin of a gravitational wave (GW) source. However, parameter degeneracies, such as the well-known mass-spin degeneracy, can complicate the interpretation of GW source parameters. The advancement in waveform models have prompted investigations into potential degeneracies between eccentricity and spin precession. Although some state-of-the-art models include these effects individually, models that incorporate spin precession and eccentricity remain in their infancy. Until models faithfully cover the complete parameter space of compact binary coalescences, our ability to accurately measure source parameters and infer binary formation channels remains limited. Here, we present a study of the distinguishability of these two key parameters. We conduct parameter estimation on mismatch-informed injections generated with SEOB waveforms. We find a localized degeneracy between eccentricity and spin precession, most prominent in shorter signals, i.e., those emitted by heavier systems. We provide quantitative estimates of its strength and identify regions of parameter space where it can be observed.