Possible explanation of the electron positron anomaly at 17 MeV in 8Be transitions

The Atomki facility in Debrecen, Hungary, has observed a significant excess
in electron positron pair production in 8Be transitions corresponding to a
possible intermediate particle of a mass of about 17 MeV. It will be
reviewed why very light still unknown particles can have escaped detection
up to now, and where they may be discovered. The nuclear transitions within
8Be will be introduced. Various possible explanations for the observed
anomaly will be presented, and why these explanations can be consistent with
constraints from other experiments.