An Anderson-like model of the QCD chiral transition

TL;DR

This paper models the QCD chiral transition using an Anderson-like Hamiltonian, linking chiral symmetry restoration and eigenmode localisation to deconfinement, and introduces a toy model that reproduces key spectral features.

Contribution

It introduces a novel Anderson-like Hamiltonian framework for finite-temperature QCD and a simplified toy model capturing essential dynamical features of chiral symmetry and localisation.

Findings

The toy model reproduces QCD spectral features in both phases.

Chiral symmetry restoration and localisation are closely related.

Both phenomena are triggered by the deconfinement transition.

Abstract

We study the problems of chiral symmetry breaking and eigenmode localisation in finite-temperature QCD by looking at the lattice Dirac operator as a random Hamiltonian. We recast the staggered Dirac operator into an unconventional three-dimensional Anderson Hamiltonian ("Dirac-Anderson Hamiltonian") carrying internal degrees of freedom, with disorder provided by the fluctuations of the gauge links. In this framework, we identify the features relevant to chiral symmetry restoration and localisation of the low-lying Dirac eigenmodes in the ordering of the local Polyakov lines, and in the related correlation between spatial links across time slices, thus tying the two phenomena to the deconfinement transition. We then build a toy model based on QCD and on the Dirac-Anderson approach, replacing the Polyakov lines with spin variables and simplifying the dynamics of the spatial gauge links, but preserving the above-mentioned relevant dynamical features. Our toy model successfully reproduces the main features of the QCD spectrum and of the Dirac eigenmodes concerning chiral symmetry breaking and localisation, both in the ordered (deconfined) and disordered (confined) phases. Moreover, it allows us to study separately the roles played in the two phenomena by the diagonal and the off-diagonal terms of the Dirac-Anderson Hamiltonian. Our results support our expectation that chiral symmetry restoration and localisation of the low modes are closely related, and that both are triggered by the deconfinement transition.