Operator product expansion

Summary

The operator product expansion writes the product of two local fields at nearby points as a sum of single local fields at one point. The coefficients are functions of the separation. Kenneth Wilson proposed it in 1969 as a general feature of quantum field theory. In a conformal field theory the coefficient functions are fixed by symmetry up to constants, and the expansion converges. So the dimensions of the fields and these constants determine all correlation functions. In two dimensions it becomes the algebraic structure of a vertex operator algebra.