Feynman Diagrams for Exam Prep: Position vs. Momentum Space

madness
Messages
813
Reaction score
69
I'm learning how to do Feynman diagrams for an exam coming up, and have come across diagrams in both position and momentum space. If I'm asked to draw a Feynman diagram without specifying which kind, is it generally assumed that it's in position space? If I label the the incoming and outgoing particles by momentum (as well as spin etc) is it then assumed that the diagram represents momentum space?
 
Physics news on Phys.org
yup correct! :)
 
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?
 
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?

bump! I would like the answer to this as well.
 
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.
 
Last edited:
Thanks a lot that's exactly what I needed to know.
 
I read Hanbury Brown and Twiss's experiment is using one beam but split into two to test their correlation. It said the traditional correlation test were using two beams........ This confused me, sorry. All the correlation tests I learnt such as Stern-Gerlash are using one beam? (Sorry if I am wrong) I was also told traditional interferometers are concerning about amplitude but Hanbury Brown and Twiss were concerning about intensity? Isn't the square of amplitude is the intensity? Please...
I am not sure if this belongs in the biology section, but it appears more of a quantum physics question. Mike Wiest, Associate Professor of Neuroscience at Wellesley College in the US. In 2024 he published the results of an experiment on anaesthesia which purported to point to a role of quantum processes in consciousness; here is a popular exposition: https://neurosciencenews.com/quantum-process-consciousness-27624/ As my expertise in neuroscience doesn't reach up to an ant's ear...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA
Back
Top