Instantons in cutoff theories Original Research Article

It is shown that the inhomogeneous saddle points of scale invariant theories make the semiclassical expansion sensitive to the choice of non-renormalizable operators. In particular, the instanton fugacity and the beta function of the two-dimensional non-linear sigmamodel depend on apparently non-renormalizable operators. This represents a non-perturbative breakdown of that concept of universality which is based on low dimensional operators.