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Reason of rejection

  1. Nov 20, 2009 #1


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    There's been quite a while since reading some serious physics, so i forgot some key points. The question I'm about to ask may seem trivial for a knowledgeable person, but I can't find the answer and I thought it is easier to get a right answer here, than wondering through a dozen of QFT books.

    So here goes:

    Why does the term

    [tex] \frac{e}{2} \bar{\Psi} (x) \Sigma^{\mu\nu} F_{\mu\nu}(x) \Psi (x)[/tex]

    NOT appear in the classical lagrangian for the spin 1/2 parity invariant electrodynamics ?

    p.s. I hope the notation is obvous, Sigma is the spin matrix = <i/2> times the commutator of the gamma matrices, the F is the e-m field tensor and the big Psi-s are the Dirac spinors.
  2. jcsd
  3. Nov 20, 2009 #2
    There is a couple of reasons; one of them - the theory is non-renormalizable with this term.

    If you consider a usual, non secondary quantized Dirac equation, this term is allowed in dynamics of charged hadrons (protons) with an anomalous magnetic moment.
  4. Nov 22, 2009 #3


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    I don't know why they got you banned, but can you sustain your <non-renormalizability> reasoning with some article published in a peer-reviewed journal or a book on QFT/QED ?

    Thank you.

    P.S. This question is, of course, again open to other people as well, since this is (up to moderation) a free forum.

    LATE EDIT: Okay, I've seen the argumentation in the first volume of Weinberg's book on QFT. It's due to <power counting> and the nonrenormalizability is induced by the presence of the derivative in the e-m tensor.
    Last edited: Nov 23, 2009
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