Pion-Pion Wechselwirkungen in dichter/heisser Materie

Employing #pi##pi# meson exchange models we examine modifications of the #pi##pi# interaction in a dense nuclear medium and in hot hadronic matter as e.g. produced in ultrarelativistic heavy ion collisions. Within an effective scattering equation medium effects are induced by modifying the intermediate 2-pion propagator through interactions with surrounding hadrons. In the first part of this work a standard treatment of the pion propagation in cold nuclear matter is used to study s-wave #pi##pi# correlations. Already at saturation density a 2-pion bound state occurs in the #sigma#-channel of the Juelich #pi##pi# model, even leading to pion pair condensation in slightly compressed nuclear matter. It is shown, however, that constraints from chiral symmetry inhibit this mechanism. A chirally improved version of the Juelich model is constructed in which pair condensation is strongly suppressed. We apply this model to calculate the correlated 2-pion exchange contribution to the central part of the Nucleon-Nucleon potential in the nuclear medium. In the second part pion properties in a hot pion gas are investigated within the finite temperature Greens function formalism. Single-pion selfenergy and in-medium #pi##pi# scattering amplitudes are evaluated selfconsistently keeping the full off-shell dynamics of the problem. At zero pion chemical potential the medium effects turn out to be rather moderate. We furthermore calculate the thermodynamic state variables117 refs.Available from TIB Hannover: RA 831(3195) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman