@article{10_4171_dm_157,
     author = {Roman G. Shterenberg and Rupert L. Frank},
     title = {On the scattering theory of the {Laplacian} with a periodic boundary condition. {II.} {Additional} channels of scattering},
     journal = {Documenta mathematica},
     pages = {57--77},
     year = {2004},
     volume = {9},
     doi = {10.4171/dm/157},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/157/}
}