Surface sums in two-dimensional large-$N$ lattice Yang--Mills: Cancellations and explicit computation for general loops

Abstract: In the context of two-dimensional large-$N$ lattice Yang--Mills theory, we perform a refined study of the surface sums defined in the companion work [BCSK24]. In this setting, the surface sums are a priori expected to exhibit significant simplifications, because two-dimensional Yang--Mills theory is a special model admitting many known exact formulas. Thus, a natural problem is to understand these simplifications directly from the perspective of the surface sums. Towards this goal, we develop a key new tool, in the form of a surface exploration algorithm (or "peeling process") which at each step carefully selects the next edge to explore. Using this algorithm, we manage to find many cancellations in the surface sums, thereby obtaining a detailed understanding of precisely which surfaces remain after cancellation. As a consequence, we obtain many new explicit formulas for Wilson loop expectations of general loops in the large-$N$ limit of lattice Yang--Mills in two dimensions and prove a convergence result for the empirical spectral measure of any simple loop.