  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.
