Lattice simulations of QCD with $μ_B\neq0$ versus phase quenched QCD

Abstract

Previously published lattice results for QCD at $μ_B\neq0$ are compared to analytic predictions for phase quenched QCD. We observe that the strength of the sign problem in QCD is linked directly to the position of the phase transition line for pion condensation in phase quenched QCD and that the number of terms needed in the Taylor expansion approach depends on the strength of the sign problem. Together this emphasizes the physical importance of the sign problem and helps to clarify the range over which the Taylor expansion approach is practically applicable. Finally, we observe that the positions of the endpoint of the first order chiral phase transition in the QCD phase diagram found in two successive computations by Fodor and Katz are both close to the position of the phase transition line for pion condensation in phase quenched QCD.