Sign problem and phase quenching in finite-density QCD: models, holography, and lattice

TL;DR

This paper investigates the sign problem in finite-density QCD, demonstrating that phase quenching yields accurate results for many observables in large N_c limits and aligns well with lattice QCD data, with small corrections at N_c=3.

Contribution

It shows that phase quenching provides exact or near-exact results for key observables in finite-density QCD models, supported by effective and holographic models, and validated by lattice data.

Findings

Phase quenching yields exact fermionic observable results in mean-field approximation.

Gauge-invariant gluonic observables are accurately predicted beyond mean field.

Good quantitative agreement with lattice QCD results at N_c=3.

Abstract

The effect of the complex phase of the fermion determinant is a key question related to the sign problem in finite-density QCD. Recently it has been shown that ignoring the complex phase -- the phase quenching -- does not change physics in a certain region of the phase diagram when a number of colors N_c is large. In this paper we study the effect of the phase quenching within the frameworks of effective models and holographic models. We show, in a unified manner, that the phase quenching gives exact results for any fermionic observables (e.g., chiral condensate) in the mean-field approximation and for gauge-invariant gluonic observables (e.g., Polyakov loop) to one-meson-loop corrections beyond mean field. We also discuss implications for the lattice simulations and confirm good quantitative agreement between our prediction and existing lattice QCD results. Therefore the phase quenching provides rather accurate answer already at N_c=3 with small 1/N_c corrections which can be taken into account by the phase reweighting.