We consider one-dimensional Fokker-Planck and Schr\"odinger equations with a
potential which approaches a periodic function at spatial infinity. We extend
the low-energy expansion method, which was introduced in previous papers, to be
applicable to such asymptotically periodic cases. Using this method, we study
the low-energy behavior of the Green function.Comment: author-created, un-copyedited version of an article accepted for
publication in Journal of Physics A: Mathematical and Theoretica