Finite Temperature Pion Scattering to one-loop in Chiral Perturbation   Theory
  We present the pion-pion elastic scattering amplitude at finite temperature to one-loop in Chiral Perturbation Theory. The thermal scattering amplitude properly defined allows to generalize the perturbative unitarity relation to the $T\neq 0$ case. Our result provides a model independent prediction of an enhanced pion-pion low-energy phase shift with the temperature and it has physical applications within the context of Relativistic Heavy Ion Collisions. 
A.Gomez Nicola, F.J.LLanes-Estrada and J.R.Pelaez