Quark-antiquark Scattering Phase Shift and Meson Spectral Function in   Pion Superfluid
  We study the quark-antiquark scattering phase shift and meson spectral function in the pion superfluid described by the Nambu--Jona-Lasinio model. The meson mixing in the pion superfluid changes dramatically the full scattering phase shift and spreads strongly the spectral function of some of the collective modes. 
Tao Xia, Jin Hu and Shijun Mao
hep-ph nucl-th