The Veneziano amplitude in AdS 5 × S 3 from an 8-dimensional effective action

We study four-point functions of arbitrary half-BPS operators in a 4-dimensional N = 2 SCFT with flavour group SO(8) at genus-zero and strong ’t Hooft coupling, corresponding — via AdS/CFT — to the (α′ expansion of the) Veneziano amplitude on an AdS5×S3 background. We adapt a procedure first proposed by Abl, Heslop and Lipstein in the context of AdS5×S5, and postulate the existence of an effective action in terms of an 8-dimensional scalar field valued in the adjoint of the flavour group. The various Kaluza-Klein correlators can then be computed by uplifting the standard AdS/CFT prescription to the full product geometry with AdS bulk-to-boundary propagators and Witten diagrams replaced by suitable AdS5×S3 versions. After elucidating the main features of the procedure, valid at all orders in α′, we show explicit results up to order α′5. The results provide further evidence of a novel relation between AdS×S and flat amplitudes — which made its first appearance in N = 4 SYM — that is perhaps the most natural extension of the well known flat-space limit proposed by Penedones to cases where AdS and S have the same radius.