  Modifications of Casimir-Polder interactions due to confinement inside a
cylindrical cavity and due to curvature in- and outside the cavity are studied.
We consider a perfectly conducting cylindrical shell with a single particle
(atom or macroscopic sphere) located next to its interior or exterior surface,
or two atoms placed inside the shell. By employing the scattering approach, we
obtain the particle-cavity interaction and the modification of the two-particle
interaction due to the cavity. We consider both retardation and thermal
effects. While for the atoms a dipole description is sufficient, for the
macroscopic sphere we sum (numerically) over many multipole fluctuations to
compute the interaction at short separations. In the latter limit we compare to
the proximity approximation and a gradient expansion and find agreement. Our
results indicate an confinement induced suppression of the force between atoms.
General criteria for suppression and enhancement of Casimir interactions due to
confinement are discussed.
