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Question on peskin and schroeder

  1. Dec 16, 2014 #1
    If you go to page 20 and 21 where the fourier expansion of the klein-gordon field operator is derived, you'll see equation (2.27).
    Now there are some small details of this whole calculation that I'm confused about.
    I followed all the way through to (2.25), but here I feel a bit weird.
    Isn't he trying to expand Φ(p)=(constant factor)(a+a* ) and plugging this back into the fourier expression above (2.21)? However (2.27) directly contradicts this, instead he is taking Φ(p)=(constant factor)(a(p)+a*(-p) )
    I understand that this is required to make the operator hermitian, but how is this formally justified step-by-step?
    (Here I use * as a poor man's dagger)
  2. jcsd
  3. Dec 16, 2014 #2


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    This step seems to confuse a lot of people (including me the first time I saw it). But it's actually really simple...


    The expression in (2.25) is already hermitian. P&S simply perform a change of integration variable for the second term, i.e., ##p \to -p##.

    That's all it is.

    Try \dagger, e.g., ##a^\dagger##. :D
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