'Special' fourth order Feynman diagram Compton Scattering - Why is it allowed?

In summary, the conversation discusses the validity of a particular Feynman diagram for Compton scattering, which involves the interaction between an electron and a photon. It is concluded that the diagram in question is not allowed, due to a potential printing error and the fact that it involves a virtual photon propagator connecting two points.
  • #1
unscientific
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I thought the fundamental electromagnetic vertex is

fundamentalem1.png


Why is the following diagram below allowed? The 'special' feynman diagram for compton scattering ##e^- + \gamma \rightarrow e^- + \gamma## is

fundamentalem2.png
 
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  • #2
It is not.
 
  • #3
Orodruin said:
It is not.

This is taken straight from Griffith's book: "Introduction to Elementary Particles".
 
  • #4
It is still not allowed, assuming the solid lines actually represent electron propagators.
 
  • #5
Orodruin said:
It is still not allowed, assuming the solid lines actually represent electron propagators.

True. I think there is a printing error. The long vertical line is supposed to be a virtual propagator (curly line) I think.

Check http://hep.uchicago.edu/~pilcher/p237-06/hw8_sol.pdf
 
  • #6
Curly line means photon propagator, not necessarily a virtual particle.
 
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  • #7
unscientific said:
True. I think there is a printing error. The long vertical line is supposed to be a virtual propagator (curly line) I think.

Check http://hep.uchicago.edu/~pilcher/p237-06/hw8_sol.pdf
I don't see your diagram there. The last one on page 1 (rotated by 90 degrees) has a curly line = photon at the place where your diagram has an error.

It is certainly virtual independent of its type because it has two ends in the diagram.
 
  • #8
Assuming its a photon connecting the bottom to the triangle loop, its the last diagram in that list. This diagram and the one with the loop's arrows in the opposite direction exactly cancel. (Write it out, take the trace, add it up). So it is not the diagram that is zero, but the sum of the two.
 
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1. What is a fourth order Feynman diagram?

A fourth order Feynman diagram is a graphical representation of the mathematical calculations involved in a physical process in quantum field theory. It is used to calculate the probability of particle interactions and is made up of various lines, vertices, and loops.

2. Why is Compton Scattering considered a special process?

Compton Scattering is considered a special process because it involves the interaction of a photon (electromagnetic radiation) and an electron. This interaction is essential for understanding the behavior of particles at the quantum level and has significant implications in particle physics and astrophysics.

3. What makes fourth order Feynman diagrams special?

Fourth order Feynman diagrams are special because they involve four interactions between particles, making them more complex and rare compared to lower order diagrams. They are also essential for understanding high-energy processes that occur in particle accelerators and other advanced experiments.

4. Why is fourth order Feynman diagram Compton Scattering allowed?

Fourth order Feynman diagram Compton Scattering is allowed because it follows the rules of quantum field theory, which govern how particles interact with each other. The mathematical calculations involved in the diagram result in a non-zero probability for the process to occur, making it a valid and allowed phenomenon.

5. What are the practical applications of understanding fourth order Feynman diagram Compton Scattering?

Understanding fourth order Feynman diagram Compton Scattering is crucial for many practical applications in particle physics and astrophysics. It helps us understand the behavior of particles at high energies, which is essential for developing new technologies and advancing our understanding of the universe's fundamental building blocks.

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