The lattice studies in QCD demonstrate the nontrivial localization behavior of the eigenmodes of the 4D Euclidean Dirac operator considered as Hamiltonian of 4 + 1 dimensional disordered system. We use the holographic viewpoint to provide the conjectural explanation of these properties. The delocalization of all modes in the confined phase is related to the θ = π -like phenomena when the fermions are delocalized on domain walls. It is conjectured that the localized modes separated by mobility edge from the rest of the spectrum in deconfined QCD correspond to the near-horizon region in the holographic dual.
arXiv:1812.02321v2 [hep-th] 2 Jul 2019Wigner-Dyson statistics, while the localized modes do not interact at all and obey the Poisson statistics. There can be a mobility edge separating localized and delocalized modes in the d ≥ 3, where d is dimension of space. In 1 + 1 and 2 + 1 dimensions the most of modes are localized, however, there could be a few delocalized modes if the topological terms are present in the action [7][8][9][10]. For instance, these distinguished delocalized modes are responsible for the Hall conductivity in 2 + 1 case.The properties of the Dirac operator spectrum have been investigated in the lattice QCD and the results found were a bit surprising. They can be summarized as follows:• All modes are delocalized in the confined phase [11] • There is the mobility edge λ m in the deconfined phase [11,13]. Low energy modes in the deconfined phase are localized while high energy part of the spectrum is delocalized. • The mobility edge λ m (T ) at T > T c grows as the function of the temperature near the deconfinement phase transition approximately as [12] λ m (T ) = a(T − T c ) with come constant a. The fractal dimension at the localization phase transition coincides with the fractal dimension of 3D unitary Anderson model [14].