Progress in complex Langevin simulations of full QCD at nonzero density

TL;DR

This paper reports advances in applying the complex Langevin method to full QCD at nonzero density, overcoming the sign problem and enabling simulations at high densities with validation from hopping parameter expansion.

Contribution

It introduces the use of gauge cooling to stabilize complex Langevin simulations of full QCD at nonzero chemical potential, extending the method's applicability to high densities.

Findings

Successful stabilization of simulations at small lattice spacings.

Simulations valid up to saturation density.

Good convergence observed in hopping parameter expansion.

Abstract

Progress in the application of the complex Langevin method to full QCD at non-zero chemical potential is reported. The method evades the sign problem which makes naive simulations at nonzero density impossible. The procedure 'gauge cooling' is used to stabilize the simulations at small enough lattice spacings. The method allows simulations also at high densities, all the way up to saturation. Simulations in a systematic hopping parameter expansion are also performed and good convergence is observed, validating the full as well as the expanded simulations.