Wightman, A.S.; Quantum Field Theory in Terms of Vacuum Expectation Values
Phys. Rev. 101 (1956) 860;
Vacuum expectation values of products of neutral scalar field operators are discussed. The properties of these distributions arising from Lorentz invariance, the absence of negative energy states and the positive definiteness of the scalar product are determined. The vacuum expectation values are shown to be boundary values of analytic functions. Local commutativity of the field is shown to be equivalent to a symmetry property of the analytic functions. The problem of determining a theory of a neutral
scalar field given its vacuum expectation values is posed and solved.