  We explore the hypothesis that the unexplained data from LSND and MiniBooNE
are evidence for a new, heavy neutrino mass-eigenstate that mixes with the
muon-type neutrino and decays into an electron-type neutrino and a new, very
light scalar particle. We consider two different decay scenarios, one with
Majorana neutrinos, one with Dirac neutrinos; both fit the data equally well.
We find a reasonable, albeit not excellent, fit to the data of MiniBooNE and
LSND. The decaying-sterile-neutrino hypothesis, however, cleanly evades
constraints from disappearance searches and precision measurements of leptonic
meson decays, as long as $1~{\rm MeV}\gtrsim m_4\gtrsim 10$~keV. The SBN
program at Fermilab should be able to definitively test the
decaying-sterile-neutrino hypothesis.
