Unitary 4-point correlators from classical geometries

TL;DR

The paper computes HHLL four-point functions in the D1D5 CFT at strong coupling via AdS$_3$/CFT$_2$, using RR ground-state microstate geometries for the heavy operators. It establishes a perturbative holographic framework in terms of deformation parameters $b_k$ and, in a special single-mode case, an exact solution, confirming a Ward identity that links bosonic and fermionic light operators. The results show explicit moduli dependence and crucially that correlators do not decay at late times, supporting unitarity in pure states and revealing the role of multi-particle Virasoro exchanges beyond the identity block. These findings provide a concrete bridge between strong-coupling gravity and CFT dynamics, and suggest avenues to study corrections and more general heavy-state ensembles relevant to black-hole microphysics.

Abstract

We compute correlators of two heavy and two light operators in the strong coupling and large $c$ limit of the D1D5 CFT which is dual to weakly coupled AdS$_3$ gravity. The light operators have dimension two and are scalar descendants of the chiral primaries considered in arXiv:1705.09250, while the heavy operators belong to an ensemble of Ramond-Ramond ground states. We derive a general expression for these correlators when the heavy states in the ensemble are close to the maximally spinning ground state. For a particular family of heavy states we also provide a result valid for any value of the spin. In all cases we find that the correlators depend non-trivially on the CFT moduli and are not determined by the symmetries of the theory, however they have the properties expected for correlators among pure states in a unitary theory, in particular they do not decay at large Lorentzian times.