KMT-2017-BLG-2820 and the Nature of the Free-Floating Planet Population
  We report a new free-floating planet (FFP) candidate, KMT-2017-BLG-2820, with
Einstein radius $\theta_\e\simeq 6\,\muas$, lens-source relative proper motion
$\mu_\rel \simeq 8\,\masyr$, and Einstein timescale $t_\e=6.5\,$hr. It is the
third FFP candidate found in an ongoing study of giant-source finite-source
point-lens (FSPL) events in the KMTNet data base, and the sixth FSPL FFP
candidate overall. We find no significant evidence for a host. Based on their
timescale distributions and detection rates, we argue that five of these six
FSPL FFP candidates are drawn from the same population as the six point-source
point-lens (PSPL) FFP candidates found by \citet{mroz17} in the OGLE-IV data
base. The $\theta_\e$ distribution of the FSPL FFPs implies that they are
either sub-Jovian planets in the bulge or super-Earths in the disk. However,
the apparent "Einstein Desert" ($10\la\theta_\e/\muas\la 30$) would argue for
the latter. Whether each of the 12 (6 FSPL and 6 PSPL) FFP candidates is truly
an FFP, or simply a very wide-separation planet, can be determined at first
adaptive optics (AO) light on 30m telescopes, and earlier for some. If the
latter, a second epoch of AO observations could measure the projected
planet-host separation with a precision ${\cal O}(10\,\au)$. At the present
time, the balance of evidence favors the unbound-planet hypothesis.
