Spectral Function of rho in Dense and Hot Hadronic Matter
  The spectral function of rho meson in hot/dense hadronic matter is studied by taking into account the nucleon-loop on quantum hadrondynamics model level. Different from the hot pion gas effect which changes the spectral function slightly, the nucleon-antinucleon polarization (Dirac sea) makes the spectral function very sharp and shifted towards the low invariant mass region significantly due to the decreasing effective nucleon mass. 
Ji-sheng Chen, Jia-rong Li, Peng-fei Zhuang