Reduced superblocks at next-to-next-to-extremality for all half-maximally supersymmetric CFTs

Abstract

We consider mixed four-point correlators of 1/2-BPS operators $\phi_{k}$ in SCFTs with eight real Poincar\'e supercharges, namely the 3d $\mathcal{N}=4$, 4d $\mathcal{N}=2$, 5d $\mathcal{N}=1$, and 6d $\mathcal{N}=(1,0)$ theories. Using the basis of solutions to the superconformal Ward identity introduced in arXiv:hep-th/0405180, we demonstrate that the dynamical data in mixed correlators of extremality $\mathcal{E}=2$ is encoded in certain simpler ``reduced correlator" functions that admit a block expansion, in close analogy to the recent result for maximally supersymmetric CFTs in arXiv:2601.15407. These reduced blocks similarly involve ordinary blocks with shifted kinematics and reproduce what is known in 4d, generalize a known example in 6d, and offer novel results in 3d and 5d.