Pion scattering poles and chiral symmetry restoration

Using unitarized chiral perturbation theory methods, we perform a detailed analysis of the pi pi scattering poles f(0)(600) and rho(770) behavior when medium effects such as temperature or density drive the system towards chiral symmetry restoration. In the analysis of real poles below threshold, we show that it is crucial to extend properly the unitarized amplitudes so that they match the perturbative Adler zeros. Our results do not show threshold enhancement effects at finite temperature in the f(0)(600) channel, which remains as a pole of broad nature. We also implement T=0 finite-density effects related to chiral symmetry restoration, by varying the pole position with the pion decay constant. Although this approach takes into account only a limited class of contributions, we reproduce the expected finite-density restoration behavior, which drives the poles towards the real axis, producing threshold enhancement and pi pi bound states. We compare our results with several model approaches and discuss the experimental consequences, both in relativistic heavy ion collisions and in pi ->pi pi and gamma ->pi pi reactions in nuclei.