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)?

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    $\begingroup$ I just found my answer... physics.stackexchange.com/q/81414 $\endgroup$
    – dan-ros
    Jul 4 '14 at 21:46
  • $\begingroup$ 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? $\endgroup$
    – Hydro Guy
    Jul 5 '14 at 13:00