Extremal Correlators in the AdS/CFT Correspondence
E. D'Hoker, D.Z. Freedman, S.D. Mathur, A. Matusis, L. Rastelli
Abstract
The non-renormalization of the 3-point functions tr X^{k_1} tr X^{k_2} tr X^{k_3} of chiral primary operators in N=4 super-Yang-Mills theory is one of the most striking facts to emerge from the AdS/CFT correspondence. A two-fold puzzle appears in the extremal case, e.g. k_1 = k_2 + k_3. First, the supergravity calculation involves analytic continuation in the k_i variables to define the product of a vanishing bulk coupling and an infinite integral over AdS. Second, extremal correlators are uniquely sensitive to mixing of the single-trace operators tr X^k with protected multi-trace operators in the same representation of SU(4). We show that the calculation of extremal correlators from supergravity is subject to the same subtlety of regularization known for the 2-point functions, and we present a careful method which justifies the analytic continuation and shows that supergravity fields couple to single traces without admixture. We also study extremal n-point functions of chiral primary operators, and argue that Type IIB supergravity requires that their space-time form is a product of n-1 two-point functions (as in the free field approximation) multiplied by a non-renormalized coefficient. This non-renormalization property of extremal n-point functions is a new prediction of the AdS/CFT correspondence. As a byproduct of this work we obtain the cubic couplings t \phi \phi and s \phi \phi of fields in the dilaton and 5-sphere graviton towers of Type IIB supergravity on AdS_5 \times S^5.