More on the N_c-insensitivity of two-dimensional adjoint QCD

Two-dimensional adjoint QCD is astonishingly insensitive to the number of colors N_c​. Part of the reason is the singularity structure of the theory which forces many possible finite N_c contributions to vanish or cancel. From numerical studies we know that there are very small corrections at finite N_c, which begs the questions as to what sets the scale of what could be called N_c-symmetry breaking. Indeed, when considering matrix elements rather than contributions of individual single-momentum states, only one trace-diagonal finite-N_c correction remains, while several parton‑number–changing corrections vanish for as of yet unexplained reasons, suggesting that the theory may contain an additional symmetry.

In this talk I will report on progress in sorting out the mechanisms and possible symmetries responsible for the N_c-insensitivity of two-dimensional adjoint QCD. In particular, I will present evidence that the conjecture that some matrix elements only vanish between physical states is wrong.