Chiral Dynamics, Deconfinement and Thermal Dileptons
  We show that in a hot hadron gas, chiral symmetry restoration and deconfinement lead to a strong suppression of dilepton production by pion annihilation in the continuum above the $\rho-\omega-\phi$ peak. The suppression due to deconfinement persists also for annihilation reactions involving heavier mesons. 
D. Kharzeev and H. Satz