It is shown that the singularity spectrum of (generalized) position-space Feynman amplitude Δ_D_(x; λ) is confined to the extended Landau variety (introduced by Kashiwara-Kawai ,  and Kashiwara-Kawai-Stapp (0)) associated with the Feynman diagram D(0), which is obtained by replacing all the masses associated with the internal lines of D with zero, at least under the assumption that the diagram D is external.
Cite this article
Takahiro Kawai, Extended Landau Variety and the Singularity Spectrum of Position-Space Feynman Amplitudes. Publ. Res. Inst. Math. Sci. 15 (1979), no. 3, pp. 767–772DOI 10.2977/PRIMS/1195187875