Casimir effect with non-local boundary conditions

Non-local boundary conditions have been considered in theoretical high-energy physics with emphasis on one-loop quantum cosmology, one-loop conformal anomalies, Bose–Einstein condensation models and spectral branes. In the present paper, for the first time in the literature, the Wightman function, the vacuum expectation values of the field square and the energy–momentum tensor are investigated for a massive scalar field satisfying non-local boundary conditions on a single and two parallel plates. The vacuum forces acting on the plates are evaluated. Interestingly, suitable choices of the kernel in the non-local boundary conditions lead to forces acting on the plates that can be repulsive for intermediate distances. It is then possible to obtain a locally stable equilibrium value of the interplate distance stabilized by the vacuum forces.