# Difference between coupling constant and strength parameter

 P: 22 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.
 P: 1,030 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.