Role of the $a_1$ meson in dilepton production from hot hadronic matter
  Dilepton production from hot hadronic matter is studied in an effective chiral Lagrangian with pions, $\rho$-mesons, and $a_1$ mesons, We find that the production rates from reactions that involve axial-vector mesons dominate over contributions from all other reactions when the dilepton invariant mass is above 1.5 GeV. 
Chungsik Song, Che Ming Ko and Charles Gale