  Based on the canonical formalism, the dilatation symmetry is implemented to
the Fokker-Planck equation for the Wigner distribution function that describes
atomic motion in an optical lattice. This reveals the symmetry principle
underlying the recent result obtained by Lutz [Phys. Rev. A 67, 051402(R)
(2003)] on the connection between anomalous transport in the optical lattice
and Tsallis statistics in the high-energy regime.Lutz's discussion is
generalized to the nonstationary case, and the condition, under which the
solution distribution decays as a power law, is derived.
