Transport coefficients and the 2PI effective action in the large N limit
  We discuss the computation of transport coefficients in large N_f QCD and the O(N) model for massive particles. The calculation is organized using the 1/N expansion of the 2PI effective action to next-to-leading order. For the gauge theory, we verify gauge fixing independence and consistency with the Ward identity. In the gauge theory, we find a nontrivial dependence on the fermion mass. 
Gert Aarts and Jose M. Martinez Resco (Ohio State)