Phase quenching in finite-density QCD: models, holography, and lattice

TL;DR

This paper demonstrates that the phase quenched approximation in finite-density QCD is exact within a certain phase diagram region, supported by models, holography, and lattice results, simplifying studies of the sign problem.

Contribution

It proves the exactness of the phase quenched approximation in a specific phase diagram region for finite-density QCD and shows its validity across models, holography, and lattice simulations.

Findings

Phase quenching is exact to O(Nf/Nc) in a certain phase diagram region.

Lattice QCD results at Nc=3 support the approximation's validity.

1/Nc corrections can be incorporated via phase reweighting without overlap issues.

Abstract

Finite-density QCD is difficult to study numerically because of the sign problem. We prove that, in a certain region of the phase diagram, the phase quenched approximation is exact to O(Nf/Nc). It is true for any physical observables. We also consider the implications for the lattice simulations and find a quantitative evidence for the validity of the phase quenching from existing lattice QCD results at Nc=3. Our results show that the phase-quench approximation is rather good already at Nc=3, and the 1/Nc correction can be incorporated by the phase reweighting method without suffering from the overlap problem. We also show the same equivalence in effective models and holographic models.