Short-Baseline Active-Sterile Neutrino Oscillations?

We suggest the possibility that the anomalies observed in the LSND experiment and the Gallium radioactive source experiments may be due to neutrino oscillations generated by a large squared-mass difference of about 20 − 30 eV. We consider the simplest 3+1 four-neutrino scheme that can accommodate also the observed solar and atmospheric neutrino oscillations. We show that, in this framework, the disappearance of (−) νe and (−) νμ in short-baseline neutrino oscillation experiments is mainly due to active-sterile transitions. The implications of the first MiniBooNE results, appeared after the completion of this paper, are discussed in an addendum. Neutrino oscillation experiments have shown that neutrinos are massive and mixed particles (see the reviews in Refs. [1, 2, 3, 4, 5, 6, 7, 8]). The observation of νe → νμ,τ oscillations with a squared-mass difference ∆m2SOL ≃ 8× 10 −5 eV (1) in solar and reactor neutrino experiments and the observation of νμ → ντ oscillations with a squared-mass difference ∆m2ATM ≃ 2.5× 10 −3 eV (2) in atmospheric and accelerator neutrino experiments can be accommodated in the minimal framework of three-neutrino mixing, in which the three active flavor neutrinos νe, νμ, and ντ are superpositions of three massive neutrinos ν1, ν2, and ν3. This three-neutrino mixing framework cannot explain through neutrino oscillations the LSND ν̄μ → ν̄e signal [9, 10, 11, 12], which requires a squared-mass difference ∆m2LSND & 10 −1 eV . (3)