the physical states are the mass states I think.
As for the Feynman diagrams, I think they use the physical/mass states too because I can't remember ever drawing or seeing a diagram where there's been interaction states on it. they are always made with, say, an electron e rather than using the...
what is the difference between a "mass state" and an "interaction state"?
I've encountered these terms a few times with no explanation, and googling around turns up absolutely nothing. Can anyone give me a brief description of the two terms, suitable for undergraduate level?
thanks.