Susceptibilities and the phase structure of a chiral model with Polyakov loops

In an extension of the Nambu--Jona-Lasinio model where the quarks interact with the temporal gluon field, represented by the Polyakov loop, we explore the relation between the deconfinement and chiral phase transitions. The effect of Polyakov loop dynamics on thermodynamic quantities, on the phase structure at finite temperature and baryon density and on various susceptibilities is presented. Particular emphasis is put on the behavior and properties of the fluctuations of the (approximate) order parameters and their dependence on temperature and net-quark number density. We also discuss how the phase structure of the model is influenced by the coupling of the quarks to the Polyakov loop.