Lattice QCD at finite temperature and density in the phase-quenched approximation

Abstract

QCD at a finite quark-number chemical potential $\mu$ has a complex fermion determinant, which precludes its study by standard lattice QCD simulations. We therefore simulate lattice QCD at finite $\mu$ in the phase-quenched approximation, replacing the fermion determinant with its magnitude. These simulations are used to study the finite temperature transition for small $\mu$,where the position and nature of this transition are expected to be unchanged by this approximation. We look for the expected critical endpoint for 3-flavour QCD. Here, it had been argued that the critical point at zero $\mu$ would become the critical endpoint at small $\mu$, for quark masses just above the critical mass. Our simulations indicate that this does not happen, and there is no such critical endpoint for small $\mu$. We discuss how we might adapt techniques used for imaginary $\mu$ to improve the signal/noise ratio and strengthen our conclusions, using results from relatively low statistics studies.