The Axial Current in Electromagnetic Interaction
  We discussed the possibility that the charged axial currents of matter fields could be non-conserved in electromagnetic interaction at $O(e) $ order. It means that chiral symmetry is broken explicitly by electromagnetic interaction. This explicit symmetry breaking of chiral symmetry is shown to lead the mass differences between the charged and neutral particles of matter fields. 
Myung Ki Cheoun, K.S.Kim and Il-Tong Cheon (Yonsei University)