Complex saddle points and disorder lines in QCD at finite temperature and density

The properties and consequences of complex saddle points are explored in phenomenological models of QCD at nonzero temperature and density. Such saddle points are a consequence of the sign problem and should be considered in both theoretical calculations and lattice simulations. Although saddle points in finite-density QCD are typically in the complex plane, they are constrained by a symmetry that simplifies analysis. We model the effective potential for Polyakov loops using two different potential terms for confinement effects and consider three different cases for quarks: very heavy quarks, massless quarks without modeling of chiral symmetry breaking effects, and light quarks with both deconfinement and chiral symmetry restoration effects included in a pair of Polyakov-Nambu-Jona Lasinio models. In all cases, we find that a single dominant complex saddle point is required for a consistent description of the model.