Deriving the Hard Thermal Loops of QCD from Classical Transport Theory
  Classical transport theory is employed to analyze the hot quark-gluon plasma at the leading order in the coupling constant. A condition on the (covariantly conserved) color current is obtained. {}From this condition, the generating functional of hard thermal loops with an arbitrary number of soft external bosonic legs can be derived. Our approach, besides being more direct than alternative ones, shows that hard thermal loops are essentially classical. 
P.F. Kelly, Q. Liu, C. Lucchesi and C. Manuel