  We propose a Born-Infeld contribution to the $U(1)_{B-L}$ extension of the
Standard Model to explain the anomalous decay of beryllium by the X17 neutral
boson, its possible connections to dark matter and the observed MeV gamma-ray
bursts. The decay width of the $Z^0$ decay into 3$X$ and 3$\gamma$ processes
are computed, based on NA64 and ATLAS experiments data.
