Comparison of complex Langevin and mean field methods applied to effective Polyakov line models

Abstract

Effective Polyakov line models, derived from SU(3) gauge-matter systems at finite chemical potential, have a sign problem. In this article I solve two such models, derived from SU(3) gauge-Higgs and heavy quark theories by the relative weights method, over a range of chemical potentials where the sign problem is severe. Two values of the gauge-Higgs coupling are considered, corresponding to a heavier and a lighter scalar particle. Each model is solved via the complex Langevin method, following the approach of Aarts and James, and also by a mean field technique. It is shown that where the results of mean field and complex Langevin agree, they agree almost perfectly. Where the results of the two methods diverge, it is found that the complex Langevin evolution has a branch cut crossing problem, associated with a logarithm in the action, that was pointed out by Mollgaard and Splittorff.

21 pages, 12 figures

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• QCD at nonzero chemical potential: recent progress on the lattice
• Complex Langevin analysis of 2D U(1) gauge theory on a torus with a $\theta$ term