Nonlocality I: Nonlocality, singularity, and elastic scattering in   quantum fields
  Using path integrals we express the quantum nonlocality of AB-effect type in the form of singularity. The gauge-fixing term in path integrals induce the AB effect in ordinary scattering processes. This means that all scattering processes are accompanied by nonlocal effect. The formulae are then extended to theory of fields that additionally include a scalar potential. It turns out that the degree of freedom of nonlocality in quantum fields is just the degree of the ghosts. Furthermore, renormalization method can be related to this type of nonlocal effect. 
Hai-Jhun Wanng