On the Sign of the Casimir Force Between Two Bodies Coupled to a Dirac field

We apply the result of Kenneth and I. Klich, Phys. Rev. Lett.97, 160401 (2006) to derive a theorem for two objects coupled to a Dirac field. We demonstrate that a sufficient condition for the Casimir interaction to be repulsive, is for their geometric configuration to be odd under the same reflection operation considered in that work.