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Photon one point function

  1. Oct 1, 2015 #1
    In 'an introduction to quantum field theory' by peskin, he writes: To analyze the photon one-point function, note that the external photon must be attached to a QED vertex. Neglecting the external photon propagator, this amplitude is therefore:


    I really cannot justify this equation. Can anyone explain it to me?
  2. jcsd
  3. Oct 6, 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. Oct 8, 2015 #3
    Intuitively, the expression is essentially the diagram with the two fermion lines and vertex (by definition of [itex]j_{\mu}[/itex]). Note the, "neglecting the external photon propagator." If you include the photon propagator as a factor, the expression gives rise to the same diagram as if the current were to be replaced by the photon field, i.e. the photon one-point correlation function.
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