INSTANTONS AND THE 1-N EXPANSION

We show that a non-interacting gas of instantons, gives a contribution which vanishes, in QCD, exponentially with N(the number of colours). If we include some of the interactions between instantons, then the resulting dilute gas of instantons-which is now in the form that is used in practice to investigate the structure of hadrons-gives a contribution that is essentialy constant with N. Thus it is entirely consistent for both the N → ∞ limit to be useful and for the dilute gas of instantons to be relevant for the properties of hadrons. © 1980 Springer-Verlag