QCD Dirac Spectra With and Without Random Matrix Theory

Abstract

Recent work on the spectrum of the Euclidean Dirac operator spectrum show that the exact microscopic spectral density can be computed in both random matrix theory, and directly from field theory. Exact relations to effective Lagrangians with additional quark species form the bridge between the two formulations. Taken together with explicit computations in the chGUE random matrix ensemble, a series of universality theorems are used to prove that the finite-volume QCD partition function coincides exactly with the universal double-microscopic limit of chUE random matrix partition functions. In the limit where N_f and N_c both go to infinity with the ratio N_f/N_c fixed, the relevant effective Lagrangian undergoes a third order phase transition of Gross-Witten type.