At high densities and/or temperature the theory of the strong interaction between elementary particles (QCD) can be solved perturbatively. But phenomena like chiral symmetry breaking and confinement, that can be probed at high energy particle colliders are shielded from these calculations due to the divergence of the strong coupling constant. Lattice calculations are a well-established non-perturbative method. However, they are yet constrained to small densities and demand huge computing power. Therefore, Polyakov-loop-extended constituent-quark models are useful to investigate the chiral and (de)confinement phase structure and the thermodynamics of strongly-interacting matter. It is shown that the quark backreaction on the gauge-field dynamics and quantum and thermal fluctuations of quarks and mesons are crucial to achieve results that agree with non-perturbative calculations. The impact of unquenching effects in the Polyakov-loop potential on the phase structure at non-vanishing quark densities is discussed. Predictions for thermodynamics at nonzero isospin are shown. Furthermore, the reliability of those models is tested by confronting its results with lattice data on the isospin dependence of the transition temperature. The phase structure of the three-dimensional temperature - isospin - quark density phase diagram is investigated. Moreover, the process of nucleation at small temperatures and large densities is investigated and the surface tension for the phase transition calculated. Some consequences of the results for the early Universe, for heavy-ion collisions, and for proto-neutron stars are discussed.

NOTES

Dr. Rainer Stiele is a candidate for a postdoc position at the nuclear physics group.