Momentum dependence of the spectral functions in the O(4) linear sigma   model at finite temperature
  The spatial momentum dependence of the spectral function for pi and sigma at finite temperature is studied by employing the O(4) linear sigma model and adopting a resummation technique called optimized perturbation theory (OPT). 
Yoshimasa Hidaka, Osamu Morimatsu, Tetsuo Nishikawa