Physical Decomposition of Photon Angular Momentum
  We address the problem of angular momentum decomposition of a free photon. We propose a natural and physical scheme for separating the total angular momentum operator for a free photon into an orbital part and a spin part with the hope that it solves this long-standing problem and it could provide a natural basis for further study of the problem of angular momentum decomposition of a gauge field system. 
Wei-Min Sun
quant-ph hep-ph