# Why are interactions always mediated via bosons (as opposed to fermions)? [duplicate]

Weak, Strong and electromagnetic force are mediated via bosons. I've come across the Walecka-model where the exchange particles are $\sigma$ and $\omega$ mesons; bosons again. why are interactions always mediated via bosons (not fermions)?

• I just found my answer... physics.stackexchange.com/q/81414 Jul 4 '14 at 21:46
• That's true, I also had the same question, but does one interpret something like triangle diagrams? Isn't a part of the interaction mediated via fermions? Jul 5 '14 at 13:00