The effect of a magnetic flux line in quantum theory.
The nonlocal exchange of the conserved, gauge invariant quantity e (i/variant Planck's) (p(k)-(e/cA(k))L(k)), L(k)=const, k=1,2 between the charged particle and the magnetic flux line (in the k=3 direction) is responsible for the Aharonov-Bohm effect. This exchange occurs at a definite time, before the wave packets are brought together to interfere, and can be verified experimentally.