Null octagon from Deift-Zhou steepest descent

A special class of four-point correlation functions in the maximally supersymmetric Yang-Mills theory is given by square Fredholm determinant a generalized Bessel kernel. In this note, we re-express its logarithmic derivatives terms two-dimensional Riemann-Hilbert problem. We solve latter null limit making use Deift-Zhou steepest descent. reproduce exact octagonal anomalous dimension 't Hooft coupling and provide novel formulation as convolution non-linear quasiclassical phase with Fermi distribution infinite chemical potential.