Force-free interactions and nondispersive phase shifts in interferometry

Zeilinger's observation that phenomena of the Aharonov-Bohm type lead to no n-dispersive, i.e., energy-independent, phase shifts in interferometers is generalized in a new proof which shows that the precise condition for nondi spersivity is a force-free interaction. The converse theorem is disproved b y a conceptual counter-example. Applications to several nondispersive inter ference phenomena are reviewed briefly. Those fall into two classes which a re objectively distinct from each other in that in the first class phase sh irts depend only on the topology of the interfering beam paths, while in th e second class force free physical interactions take place at identifiable points along the path. Apparent disagreements in the literature about the t opological nature of the phenomena in the second class stern from differing definitions.