  Several sub-diffusive stochastic processes in nature, e.g., motion of tagged
monomer in polymers, height fluctuation of interfaces and particle dynamics in
single-file diffusion etc. can be described rigorously or approximately by the
superposition of various modes whose relaxation times are broadly distributed.
In this paper, we propose a mode analysis generating super-diffusion, which is
paired or complementary with that for sub-diffusion. The key point in our
discussion lies in the identification of a pair of conjugated variables, which
undergoes sub- and super-diffusion, respectively. We provide a simple
interpretation for the sub- and superdiffusion duality for these variables
using the language of polymer physics. The analysis also suggests the
usefulness to look at the force fluctuation in experiments, where a polymer is
driven by a constant velocity.
