Pathologies of Quenched Lattice QCD at non--zero Density and its Effective Potential

TL;DR

This paper investigates the challenges and unphysical results encountered in quenched lattice QCD simulations at non-zero baryon density, analyzing the forbidden region and effective potential to understand these pathologies.

Contribution

It provides a detailed analysis of the forbidden region in quenched lattice QCD at finite density and interprets simulation pathologies using the effective potential approach.

Findings

Large lattice size does not eliminate pathologies at weak coupling.

Effective potential analysis clarifies the nature of the forbidden region.

Strong coupling simulations offer additional insights into the issues.

Abstract

We simulate lattice QCD at non--zero baryon density and zero temperature in the quenched approximation, both in the scaling region and in the infinite coupling limit. We investigate the nature of the forbidden region -- the range of chemical potential where the simulations grow prohibitively expensive, and the results, when available, are puzzling if not unphysical. At weak coupling we have explored the sensitivity of these pathologies to the lattice size, and found that using a large lattice ($64 \times 16^3$) does not remove them. The effective potential sheds considerable light on the problems in the simulations, and gives a clear interpretation of the forbidden region. The strong coupling simulations were particularly illuminating on this point.