  The MiniBooNE experiment has observed a significant excess of electron
neutrinos in a muon neutrino beam at source-detector distances too short to be
compatible with standard neutrino oscillations. The most straightforward
explanation for this signal in terms of oscillations between Standard Model
neutrinos and a new, sterile, neutrino, is disfavored by null results from
experiments looking for muon neutrino disappearance. Here, we discuss the
possibility that MiniBooNE data are instead explained by a sterile neutrino
that decays quickly back into active neutrinos plus a light boson. The flavor
composition of the secondary neutrinos is determined by the sterile neutrino
mixing angles, and we show that the data is best explained if the sterile
neutrino mixes mostly with electron neutrinos. The preferred range for the mass
of the sterile neutrino is between 100 eV and 1 keV. We argue that the model
can easily satisfy cosmological constraints because it has the "secret
interactions" mechanism built-in. Accommodating in addition to the MiniBooNE
anomaly also the LSND, reactor, and gallium anomalies is possible, but in this
case the model needs to be extended to avoid cosmological limits.
