Abstract

The pressure and energy density of the quark-gluon plasma at finite baryon chemical potential are calculated using the Complex Langevin equation. The stout smearing procedure is generalized for the SL(3,$\mathcal{C}$) manifold allowing the usage of an improved action in the Complex Langevin setup. Four degenerate flavors of staggered quarks with $m_\pi=500-700$ MeV are used with a tree-level Symanzik improved gauge action on $16^3 \times 8 $ lattices. Results are compared to the Taylor expansion and good agreement is found for small chemical potentials.

Highlights

  • AND OVERVIEWThe strong interactions are described by quantum chromodynamics (QCD)

  • The lattice formulation of QCD suffers from a problem at nonzero chemical potential: the partition sum of the theory is written in terms of a complex measure due to the fermion determinant, the standard importance sampling approaches are invalid

  • The aim of the study is to establish new methods offered by the availability of the complex Langevin equation (CLE) simulations at μ > 0 where naive importance sampling calculations are invalidated by the sign problem

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Summary

INTRODUCTION

The determination of the QCD phase diagram is one of the great challenges of the theoretical study of this theory. The lattice formulation of QCD suffers from a problem at nonzero chemical potential: the partition sum of the theory is written in terms of a complex measure due to the fermion determinant, the standard importance sampling approaches are invalid. This is called the QCD sign problem.

THE COMPLEX LANGEVIN EQUATION
THERMODYNAMICS AT NONZERO CHEMICAL POTENTIAL
STOUT SMEARING
RESULTS
CONCLUSIONS
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