Abstract
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.
Highlights
Many major discoveries in neutrino physics have started out as oddball anomalies that gradually evolved into incontrovertible evidence
We propose a different explanation for the MiniBooNE anomaly, and possibly for the LSND, reactor, and gallium anomalies
Putting MiniBooNE into context with other νe appearance searches, we show in Fig. 3 two slices through the 5-dimensional parameter space of the decaying sterile neutrino model along the plane spanned by jUe4j2 and jUμ4j2
Summary
Many major discoveries in neutrino physics have started out as oddball anomalies that gradually evolved into incontrovertible evidence. If νs has small but nonzero mixing with both νe and νμ and if the corresponding mostly sterile neutrino mass eigenstate ν4 is somewhat heavier (∼1 eV) than the Standard Model neutrinos, the MiniBooNE signal could be explained. This explanation would be consistent with a similar 3.8σ anomaly from the. We will see that this scenario requires only very small mixing between νs and νμ, avoiding the strong νμ disappearance constraints It requires somewhat larger mixing between νs and νe, in line with the hints from reactor and radioactive source experiments. We will argue that decaying sterile neutrinos may avoid cosmological constraints because the model automatically endows sterile neutrinos with self-interactions (“secret interactions” [25,26])
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