Pathologies of quenched lattice QCD at nonzero density and its effective potential

Abstract

We simulate lattice QCD at nonzero 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 explore the sensitivity of these pathologies to the lattice size, and find that using a large lattice (64×${16}^3$) 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 are particularly illuminating on this point.