I am trying to understand to which realistic objects one can apply the definition of single-particle states as irreducible representations of the Poincare group. Let me start with a couple of motivational questions.
In $\phi^4$ theory, would we call the states of definite momentum and energy single-particle states?
What are the single-particle states in a theory like QCD, with multiple fields and various charges? Are those what we intuitively think of as "dressed quarks"/"dressed gluons" or do "bound states" count as well?
My intuitive understanding is that one should call a single-particle state the state with the maximum number of charges being defined. For example, in QED, I would say that the single-particle states are the states of definite energy, momentum, and electric charge. How does the presence of multiple fields and charges affect the definition?
I am not asking "what do we call a particle in QCD?", but rather "what is the physical meaning of states defined in Weinberg (2.5.1)?" and "how does this definition work for theories with multiple fields"?