Helicity Entanglement of Moving Bodies
  We investigate the Lorentz transformation of the reduced helicity density matrix for a pair of massive spin 1/2 particles. The corresponding Wootters concurrence shows no invariant meaning, which implies that we can generate helicity entanglement simply by the transformation from one reference frame to another. The difference between the helicity and spin case is also discussed. 
Shuxin Shao, Song He, and Hongbao Zhang