Quenched QCD at finite density

Abstract

Simulations of quenched $QCD$ at relatively small but {\it nonzero} chemical potential $μ$ on $32 \times 16^3$ lattices indicate that the nucleon screening mass decreases linearly as $μ$ increases predicting a critical chemical potential of one third the nucleon mass, $m_N/3$, by extrapolation. The meson spectrum does not change as $μ$ increases over the same range, from zero to $m_π/2$. Past studies of quenched lattice QCD have suggested that there is phase transition at $μ= m_π/2$. We provide alternative explanations for these results, and find a number of technical reasons why standard lattice simulation techniques suffer from greatly enhanced fluctuations and finite size effects for $μ$ ranging from $m_π/2$ to $m_N/3$. We find evidence for such problems in our simulations, and suggest that they can be surmounted by improved measurement techniques.