Reformulation of finite-temperature dilepton production

The multiplicity of $e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$ pairs produced at finite temperature is expressed in terms of the photon proper self-energy at finite temperature. The production rate is strongly dependent on the four-momentum $q^{\mu }$ of the lepton pair and has a resonance at $q^2=\mathrm{Re}\Pi$.