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Calculation in Peskin&Schroeder QFT book

  1. Oct 22, 2011 #1


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    Hi, i can't get the result stated as equation (2.33) in page 22. To be more clear, after the elimination of the divergent commutator, i still have two extra terms that i don't know how to cancel out. the total extra term is ap.a(-p)-a^+(-p).a^+p. :confused:
  2. jcsd
  3. Jun 30, 2012 #2
    I think the extra terms are
    [tex]{\bf{P}}({a_{\bf{p}}}{a_{ - {\bf{p}}}} - {a^ + }_{ - {\bf{p}}}{a^ + }_{\bf{p}})[/tex]
    Notice that they are both odd function since a_p and a_(-p) are commute. Thus, the integration of them should be ZERO.
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