A note on the exact Green function for a quantum system decorated by two or more impurities

Producción CientíficaThe exact Green function is constructed for a quantum system, with known Green function, which is decorated by two delta function impurities. It is shown that when two such impurities coincide they behave as a single singular potential with combined amplitude. The results are extended to N impurities and higher dimensions.Ministerio de Economía, Industria y Competitividad (project ct MTM2014-57129-C2-1)Junta de Castilla y León (project VA057U