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Difference between coupling constant and strength parameter

  1. Aug 25, 2014 #1
    Hello to everyone,

    I got a little bit confused between the coupling constant [itex]g_W[/itex] and the strength parameter [itex]\alpha_W[/itex] in the weak interaction. For what I know they should both give an idea of the strength of the interaction but I miss to understand what's the difference between them.
  2. jcsd
  3. Aug 25, 2014 #2


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    Gold Member

    If I understand your quantities well...alpha is called the (running) coupling constant too.
    There is no difference between the one or the other...
    [itex] \alpha_{W}= \frac{g_{W}^{2}}{4 \pi}[/itex]

    The one appears on the Lagrangian as the coupling strength between the fields on vertices.
    The other appears in the Feynman diagrams of interactions when you have two vertices.
  4. Aug 25, 2014 #3
    Thank you for the answer!
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