Virtual bremsstrahlung from pions and quarks in thermalized hadronic   matter
  A soft photon approximation is used to calculate the rates of lepton pair production through virtual bremsstrahlung from both pions and quarks. Standard assumptions about the evolution of a nuclear system under collision allow pion and quark driven total production to be calculated. Comparisons are made with Dalitz decay of light mesons. These mechanisms are expected to be significant contributors to the soft dilepton mass spectra one might observe in heavy ion collisions at RHIC and LHC energies. 
K. Haglin, C. Gale and V. Emel'yanov