The QCD phase diagram in the limit of heavy quarks using complex Langevin dynamics

TL;DR

This paper uses complex Langevin dynamics to explore the QCD phase diagram with heavy quarks, addressing the sign problem and analyzing gauge cooling techniques to distinguish between confined and deconfined phases.

Contribution

It applies complex Langevin simulations to heavy-quark QCD, evaluates gauge cooling effectiveness, and maps the phase boundary between confined and deconfined states.

Findings

Gauge excursions affect observable distributions.

Small excursions yield consistent phase boundary results.

Adaptive gauge cooling can prevent large excursions.

Abstract

Complex Langevin simulations allow numerical studies of theories that exhibit a sign problem, such as QCD, and are thereby potentially suitable to determine the QCD phase diagram from first principles. Here we study QCD in the limit of heavy quarks for a wide range of temperatures and chemical potentials. Our results include an analysis of the adaptive gauge cooling technique, which prevents large excursions into the non-compact directions of the SL($3, \mathbb{C}$) manifold. We find that such excursions may appear spontaneously and change the statistical distribution of physical observables, which leads to disagreement with known results. Results whose excursions are sufficiently small are used to map the boundary line between confined and deconfined quark phases.