Several theorems about the interference of particle beams and the theoretical interpretation of Collela-Overhauser-Werner and Marton experiments.

A new theorem about the interference between particle beams is established. The Collela-Overhauser-Werner and Marton experiments are theoretically explained with a theorem established by Chiu and Stodolsky. The Feynman theory is applied to obtaining the propagator for a particle beam in a gravitational field, and the Collela-Overhauser-Werner experiment is further analyzed. Another theorem, established by Chiu and Stodolsky, and our new theorem are proved with the method of Feynman's path integrals.