Chiral phase transition: the role of scalar fields

Full text: The interpretation of scalar mesons in the vacuum is a highly debated topic. In the context of a linear sigma model it is not clear which is the scalar resonance listed in the PDG which should be identified with the sigma field of the model. This identification is not only an issue of vacuum's phenomenology: in fact, it has a strong influence on the properties of the system at nonzero temperature and density, most notably on the chiral phase transition. In this talk different scenarios are presented and discussed. Also, the inclusion of an additional, light scalar field in the Lagrangian, to be interpreted as a tetraquark field as suggested by many studies in the vacuum, is here investigated at nonzero T with special attention to its role on the chiral phase transition. (author)