Composite field
In quantum field theory, a composite field is a field defined in terms of other more "elementary" fields. It might describe a composite particle (bound state) or it might not. It might be local, or it might be nonlocal. Noether fields are often composite fields and they are local.
In the generalized LSZ formalism, composite fields, which are usually nonlocal, are used to model asymptotic bound states.
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