Damping of energetic gluons and quarks in high-temperature QCD

When a gluon or a quark is sent through the hot QCD plasma it acquires a damping rate that is given by γ(p)=cg2 ln(1/g)T+O(g2T) for ‖p‖≫gT. We show that very simple arguments suffice to fix the numerical coefficient c in this expression and to show that the O(g2T) contributon is incalculable in perturbation theory without further assumptions. For QCD with Nc colors we find cg=+Nc/4π for gluons and cq=+(Nc2-1)/8πNc for quarks, in agreement with more detailed calculations of Pisarski et al. but not with those of Lebedev et al. The simplicity of the calculation permits a direct verification of the gauge invariance and the physical sign of the result.