Duality and Chiral Restoration from Dilepton Production in Relativistic Heavy-Ion Collisions

We discuss the recent status in the theoretical understanding of dilepton production in central heavy-ion reactions with the Pb-beam at the full CERN-SpS energy of 158 AGeV. In the low-mass region ($M\le$~1 GeV) a strong broadening of the vector meson resonances in hot and dense matter (especially for the $\rho$ meson) entails thermal dilepton rates very reminiscent to perturbative $q\bar{q}$ annihilation close to the expected phase boundary of the chiral symmetry restoring transition. A consistent description of the experimentally observed enhancement at both low and intermediate masses (1.5 GeV~$\le M\le$~3 GeV) in terms of thermal radiation from an expanding fireball can be obtained.