Pion Decay Constant at Finite Temperature in the Nonlinear Sigma Model
  We calculate the pion decay constant near the critical temperature of the $O(N)$ nonlinear sigma model in the large $N$ limit. Making use of the known low temperature behavior, we construct a Pad\'{e} approximant to obtain the behavior of $f_\pi(T)$ at all temperatures. 
Sangyong Jeon and Joseph Kapusta (University of Minnesota)