Electromagnetic two-point functions and Casimir densities for a
  conducting plate in de Sitter spacetime
  We evaluate the two-point function for the electromagnetic field tensor in
$(D+1)$-dimensional de Sitter spacetime assuming that the field is prepared in
Bunch-Davies vacuum state. This two-point function is used for the
investigation of the vacuum expectation values (VEVs) of the field squared and
the energy-momentum tensor in the presence of a conducting plate. The VEVs are
decomposed into the boundary-free and plate-induced parts. For the latter,
closed form analytical expressions are given in terms of the hypergeometric
function. For $3\leqslant D\leqslant 8$ the plate-induced part in the VEV of
the electric field squared is positive everywhere, whereas for $D\geqslant 9$
it is positive near the plate and negative at large distances. The VEV of the
energy-momentum tensor, in addition to the diagonal components, contains an
off-diagonal component which corresponds to the energy flux along the direction
normal to the plate. Simple asymptotic expressions are provided at small and
large distances from the plate compared with the de Sitter curvature scale. For
$D\geqslant 4$, all the diagonal components of the plate-induced vacuum
energy-momentum tensor are negative and the energy flux is directed from the
plate.
