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The gravitational microlensing technique is most sensitive to planets in aJupiter-like orbit and has detected more than 200 planets. However, only a fewwide-orbit ($s > 2$) microlensing planets have been discovered, where $s$ isthe planet-to-host separation normalized to the angular Einstein ring radius,$\theta_{\rm E}$. Here we present the discovery and analysis of a strongcandidate wide-orbit microlensing planet in the event, OGLE-2017-BLG-0448. Thewhole light curve exhibits long-term residuals to the static binary-lenssingle-source model, so we investigate the residuals by adding the microlensingparallax, microlensing xallarap, an additional lens, or an additional source.For the first time, we observe a complex degeneracy between all four effects.The wide-orbit models with $s \sim 2.5$ and a planet-to-host mass-ratio of $q\sim 10^{-4}$ are significantly preferred, but we cannot rule out the closemodels with $s \sim 0.35$ and $q \sim 10^{-3}$. A Bayesian analysis based on aGalactic model indicates that, despite the complicated degeneracy, thesurviving wide-orbit models all contain a super-Earth-mass to Neptune-massplanet at a projected planet-host separation of $\sim 6$ au and the survivingclose-orbit models all consist of a Jovian-mass planet at $\sim 1$ au. The hoststar is probably an M or K dwarf. We discuss the implications of thisdimension-degeneracy disaster on microlensing light-curve analysis and itspotential impact on statistical studies.

OGLE-2017-BLG-0448Lb: A Low Mass-Ratio Wide-Orbit Microlensing Planet?