Instantons and non-renormalisation in AdS/CFT

The series of perturbative fluctuations around a multi-instanton contribution to a specific class of correlation functions of supercurrents in N=4 supersymmetric SU(N) Yang-Mills theory is examined in the light of the AdS/CFT correspondence. Subject to certain plausible assumptions, we argue that a given term in the 1/N expansion in such a background receives only a finite number of perturbative corrections in the 't Hooft limit. Such instanton non-renormalisation theorems would explain, for example, the exact agreement of certain weak coupling Yang-Mills instanton calculations with the strong coupling predictions arising from D-instanton effects in string theory amplitudes. These non-renormalisation theorems essentially follow from the assumption of a well defined derivative (α') expansion in the string theory dual of the Yang-Mills theory. (author)