The problem of Chiral Restoration and Dilepton Production in Heavy Ion Collisions

Abstract

In the lecture we review several issues related to recent development in non-perturbative QCD. The ``instanton liquid model'' reproduces not only the basic vacuum parameters (the condensates), but even hadronic correlators. New information obtained from lattice simulations also confirm it. Meanwhile the model itself was developed into a self-consistent approach, allowing to include 't Hooft interaction to all orders. It was also generalized to non-zero temperatures and high densities. We discuss one issue, displayed by behavior of the pion and rho correlation functions: the former has strong non-perturbative effects at small distances, the latter has none. What happens at $T\sim T_c$ can be answered by dilepton production experiments with heavy ion collisions. The results definitely indicate large changes in spectral density and "melting" of the rho meson peak, possibly reaching the rate corresponding to complete chiral restoration.