Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

  1. Mar 25, 2015 #1
    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
     
  2. jcsd
  3. Mar 25, 2015 #2

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    It is not.
     
  4. Mar 25, 2015 #3
    This is taken straight from Griffith's book: "Introduction to Elementary Particles".
     
  5. Mar 25, 2015 #4

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    It is still not allowed, assuming the solid lines actually represent electron propagators.
     
  6. Mar 25, 2015 #5
    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
     
  7. Mar 25, 2015 #6

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Curly line means photon propagator, not necessarily a virtual particle.
     
  8. Mar 25, 2015 #7

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    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.
     
  9. Mar 26, 2015 #8

    Hepth

    User Avatar
    Gold Member

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: 'Special' fourth order Feynman diagram Compton Scattering - Why is it allowed?
  1. Feynman Diagram (Replies: 2)

  2. Feynman Diagram (Replies: 11)

  3. Feynman diagram (Replies: 1)

Loading...