Thermal properties of interacting hadrons

We study hadronic matter at temperatures close to the pion mass. In the dilute-gas stage, the relativistic virial expansion is used with empirical phase shifts to investigate the thermodynamic properties of an interacting gas of pions, kaons and nucleons. The interplay between the attractive and repulsive interactions which governs the size of the interacting contributions is discussed. In the dense gas stage characterized by the presence of many massive resonances, schematic models that include the effects of repulsive interactions are analysed. Limits on the size of repulsive interactions are established by causality constraints. The causal behaviour of some of the conventional excluded-volume approaches is examined. Since our work is also aimed at studying those equations of state which may be used in dynamical simulations of heavy-ion collisions, phase diagrams are constructed including the thermodynamics of the quark-gluon phase.