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In quantum field theory, correlation functions, often referred to as correlators or Green's functions, are vacuum expectation values of time-ordered products of field operators. They are a key object of study in quantum field theory where they can be used to calculate various observables such as S-matrix elements, although they are not themselves…
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| Subject | Predicate | Object | Confidence | Src |
|---|---|---|---|---|
| S-matrix elements | instance of | They are a key object of study in quantum field theory where they can be used to calculate various observables | 0.80 | text |
| although they are not themselves observables | instance of | They are a key object of study in quantum field theory where they can be used to calculate various observables | 0.80 | text |
| one-particle irreducible correlation functions.In the path integral formulation | instance of | By excluding other sets of diagrams one can define other correlation functions | 0.80 | text |
| n-point correlation functions are written as a functional average G n | instance of | By excluding other sets of diagrams one can define other correlation functions | 0.80 | text |
| polarization vectors for photons or spinor states for fermions | instance of | For non-scalar theories the reduction formula also introduces external state terms | 0.80 | text |
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