A consistent interpretation of the Karmen anomaly
  The Karmen anomaly can be interpreted as being due to a heavy neutrino of mass around 137 MeV produced in $\pi_{e 2}$ decays. This interpretation is consistent with the present limits on the couplings of such an object. 
J.-M. Levy and F. Vannucci (Laboratoire de Physique Nucleaire et de   Hautes Energies, Paris, France)