Electromagnetic properties of neutral and charged spin 1 particles
  The structure of the electromagnetic vertex of spin-1 particles are studied in a general way, for the diagonal as well as the off-diagonal couplings. In each case, we consider in detail the consequences of gauge invariance and the space-time discrete symmetries, paying particular attention to the implications for the couplings of the photon to neutral gauge bosons, which arise in higher orders. Several general results concerning the static electromagnetic properties of neutral bosons are derived, analogous to the results that are well known in the case of neutral spin-1/2 particles. 
Jose F. Nieves and Palash B. Pal