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What is coupling in QFT?

  1. Nov 16, 2014 #1
    I'm an experimentalist, so go easy on me... What does it mean for a particle to either couple or not couple to a field? I haven't taken a class in QFT yet, so please try to explain the general idea without any details or equations!
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  3. Nov 16, 2014 #2


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    As an experimentalist as well, my working understanding is that you may replace "couple" with "interact". E.g. W± couples with the electromagnetic field = W± interacts with the electromagnetic field.
  4. Nov 16, 2014 #3


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    In the Lagrangian, the coupling between two fields is a term in which the two fields are multiplied together. A free scalar field has only up to quadratic terms, so if one adds cubic or higher order terms, those are sometimes said to be self-interaction terms. http://www.damtp.cam.ac.uk/user/tong/qft/three.pdf gives an example of a self-interaction term (Eq 3.5), and an example of an interaction between two different types of fields (3.7)
  5. Nov 17, 2014 #4
    An example: particles with electric charge couple to the electromagnetic field. Electrically neutral particles do not couple to the electromagnetic field.
  6. Nov 17, 2014 #5


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    The terminology is rather: free fields couple to each other, while particles interact with each other. So in QFT to say <a particle couples to a field> is illegal. Within classical electrodynamics we say <particles are acted upon by electromagnetic fields>.
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