On the two kinds of vector particles
  All known elementary vector particles, the photon, Z, W and the gluons, are described by the gauge theory. They belong to the real representation (1/2,1/2) of the Lorentz group. On the other hand inequivalent representations (1,0) and (0,1) also correspond to particles with spin 1. It is natural to suppose that, along with the known vector particles, the new particles can exist. Evidence for the existence of these particles in nature is the presence of the axial-vector meson resonances with quantum numbers 1^{+-}. Other indications for their existence are discussed. The signatures of their contributions into different physical processes are presented. 
M. V. Chizhov