  We discuss the large scale effective potential for elastic objects
(manifolds) in the presence of a random pinning potential, from the point of
view of the Functional Renormalisation Group (FRG) and of the replica method.
Both approaches suggest that the energy landscape at large scales is a
succession of parabolic wells of random depth, matching on singular points
where the effective force is discontinuous. These parabolas are themselves
subdivided into smaller parabolas, corresponding to the motion of smaller
length scales, in a hierarchical manner. Consequences for the dynamics of these
pinned objects are underlined.
