The discussion revolves around the differences between Feynman diagrams in position space and momentum space, particularly in the context of preparing for an exam. Participants explore how to interpret diagrams when not explicitly labeled and the implications of drawing them in different spaces.
Participants generally agree on the assumption regarding the default space for Feynman diagrams and the topological equivalence of diagrams in different spaces, but there is ongoing exploration of the implications of these differences.
Some assumptions regarding the interpretation of diagrams and the mathematical expressions involved may not be fully articulated, leading to potential gaps in understanding the nuances of the discussion.
madness said:What is the difference when drawing diagrams in momentum space and position space? In my notes the 2 lowest order diagrams for Compton scattering look quite different in momentum and position space. In position space the internal electron line in the second diagram points horizontally in position space and vertically in momentum space. What does this mean?
The actual diagrams are the same in every basis, only the mathematical expressions representing the diagrams are different. As for your question about the internal electron line: if two diagrams only differ by some sort of rotation of propagator lines, the diagrams are the same (topologically equivalent), since when you write down the mathematical expression for the diagram, all that matters is the relative positioning of vertices and lines. The orientation of lines does not step into equations.madness said:What is the difference when drawing diagrams in momentum space and position space? In my notes the 2 lowest order diagrams for Compton scattering look quite different in momentum and position space. In position space the internal electron line in the second diagram points horizontally in position space and vertically in momentum space. What does this mean?