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Correlation function (quantum field theory)
Expectation value of time-ordered quantum operators / From Wikipedia, the free encyclopedia
For other uses, see Correlation function (disambiguation).
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. They are closely related to correlation functions between random variables, although they are nonetheless different objects, being defined in Minkowski spacetime and on quantum operators.