Hegerfeldt's theorem is a no-go theorem that demonstrates the incompatibility of the existence of spatially localized discrete particles with the combination...

Hegerfeldt's theorem implies that localizable free particles are incompatible with causality in relativistic quantum theory. Coleman–Mandula theorem states...

that operator. It also has several famous strange behaviors (see the Hegerfeldt theorem in particular), one of which is seen as the motivation for having...