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ELI5: Antiparticles in Feynman Diagrams

  1. Nov 16, 2015 #1
    Hi!, Im studying for an introductory course in QED and Feynman Diagrams. Everything we see is like a first order approach and im having some trouble understanding antiparticles in Feynman Diagrams:
    Why is it that we put an antiparticle that is leaving as if it is entering the interaction??
    This is:
    We have the interaction term:
    [tex]\bar{\Phi}\gamma^{\mu} \Phi A_{\mu}[/tex]
    From which I understood that [tex]\bar{\Phi}[/tex] corresponds to the outgoing particle. Yet for antiparticles we draw them as entering.

    Also, i dont fully understand why we use the adjoint (i.e: with [tex]\gamma^0[/tex] multiplying) as the outgoing particles. I thought we were calculating interactions elements for the Hamiltonian. I dont know where the [tex]\gamma^0[/tex] comes from.

    Sorry for my english.
    Last edited: Nov 16, 2015
  2. jcsd
  3. Nov 21, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Nov 22, 2015 #3

    A. Neumaier

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    Science Advisor

    Feynman diagrams describe multiple integral contributing to the scattering amplitude, they don't depict events in time. (The latter is only a superficial mnemonics.) See, e.g., http://physics.stackexchange.com/a/22064/7924

    The direction of the arrows comes from the direction of the momentum vector in the Fourier transform of the integrals they depict. The Fourier transform treats particle and antiparticles in a way reflecting the CTP symmetry: changing p to -p changes particles to antiparticle and reverses the signs of all charges.
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