Electromagnetic Casimir effect for conducting plates in de Sitter spacetime

Two-point functions, the mean field squared and the vacuum expectation value (VEV) of the energy-momentum tensor are investigated for the electromagnetic field in the geometry of parallel plates on background of (D + 1)-dimensional dS spacetime. We assume that the field is prepared in the Bunch-Davies vacuum state and on the plates a boundary condition is imposed that is a generalization of the perfectly conducting boundary condition for an arbitrary number of spatial dimensions. It is shown that for D. 4 the background gravitational field essentially changes the behavior of the VEVs at separations between the plates larger than the curvature radius of dS spacetime. At large separations, the Casimir forces are proportional to the inverse fourth power of the distance for all values of spatial dimension D >= 3. For D >= 4 this behavior is in sharp contrast with the case of plates in Minkowski bulk where the force decays as the inverse (D + 1)th power of the distance.