In quantum field theory, the concept of a force is not explicitly present, and we speak of interactions. I guess we could say that a force is an emergent phenomenon.
Interactions manifest themselves in (at least) three important ways: particle decay, scattering and forces.
In (introductory) QFT, typically the first two, particle decay and scattering processes, are treated extensively and computations are made, but forces, e.g. the repulsion between two fermions, or bound systems, are usually not studied. My questions:
What is the reason for that? One possible reason I could think of is that for forces we need the concept of a localized particle, whereas in QFT it seems that we mostly work in the momentum representation. Maybe it is just much more complex (for this reason or others) to study forces than decay and scattering.
Is it possible to see, not necessarily very formally, how an attractive or repulsive force could emerge from an interaction Lagrangian?