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 $D\geq 4$ 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 $D\geq 3$. For $D\geq 4$ 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.
