The stability of the QED vacuum in the temporal gauge
  The stability of the vacuum for QED in the temporal gauge will be examined. It is generally assumed that the vacuum state is the quantum state with the lowest energy. However, it will be shown that this is not the case for a system consisting of a fermion field coupled to a quantized electromagnetic field in the temporal gauge. It will be shown that for this situation there exist quantum states with less energy than the vacuum state. 
Dan Solomon