The MiniBooNE anomaly and heavy neutrino decay

The anomaly in the low energy distribution of quasi-elastic neutrino events reported by the MiniBooNE collaboration is discussed. We show that the observed excess of electron-like events could originate from the production and decay of a heavy neutrino ($\nu_h$) in the MiniBooNE detector. The $\nu_h$ is created by mixing in $\nu_\mu$ neutral-current interactions and decays radiatively into $\nu \gamma$ due to a transition magnetic moment between the $\nu_h$ and a light neutrino $\nu$. The energy measured in the detector arises from the subsequent conversion of the decay photon into a $\pair$ pair within the detector volume. The analysis of the energy and angular distributions of the excess events suggests that the $\nu_h$ has a mass around 500 MeV and the lifetime $\tau_{\nu_h} \lesssim 10^{-9}$ s. Existing experimental data are found to be consistent with a mixing strength between the $\nu_h$ and the $\nu_\mu$ of $|U_{\mu h}|^2 \simeq (1-4)\times 10^{-3}$ and a $\nu_h$ transition magnetic moment of $\mu_{tr} \simeq (1- 6)\times 10^{-9} \mu_B$. Finally, we discuss the reason why no significant excess of low energy events has been observed in the recent antineutrino data.