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.
