The operator product expansion converges in perturbative field theory

Understand

We show, within the framework of the Euclidean $\phi^4$-quantum field theory in four dimensions, that the Wilson operator product expansion (OPE) is not only an asymptotic expansion at short distances as previously believed, but even converges at arbitrary finite distances.

• Our proof rests on a detailed estimation of the remainder term in the OPE, of an arbitrary product of composite fields, inserted as usual into a correlation function with further "spectator fields".
• The estimates are obtained using a suitably adapted version of the method of renormalization group flow equations.
• Convergence follows because the remainder is seen to become arbitrarily small as the OPE is carried out to sufficiently high order, i.e.