# Difference between coupling constant and strength parameter

1. ### Daaavde

25
Hello to everyone,

I got a little bit confused between the coupling constant $g_W$ and the strength parameter $\alpha_W$ 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. ### ChrisVer

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

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.

3. ### Daaavde

25
Thank you for the answer!

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