Probing Hot Quantum Chromodynamics with a Complex Chemical Potential

Abstract

Quantum Chromodynamics (QCD) at finite baryon density cannot be investigated using standard Monte Carlo simulation methods because its path integral measure is complex, leading to large cancellations in expectation values. This is often called the “sign problem”. One suggestion for determining the properties of QCD at finite temperatures and densities is to carry out lattice simulations with an imaginary chemical potential whereby no sign problem arises, and to convert the results to real physical observables only afterwards. We test the feasibility of this for spatial correlation lengths in the quark-gluon plasma phase. Simulations with imaginary chemical potential followed by analytic continuation are compared with simulations with real chemical potential, using a dimensionally reduced effective action for hot QCD. We find that for imaginary chemical potential the system undergoes a phase transition at |μ/T|≈π/3, and thus observables are analytic only in a limited range. However, utilising this range, relevant information can be obtained for QCD with a real chemical potential. These results have been published in [1,2].