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/4{π} for gluons and cq=+(Nc²-1)/8{π}Nc 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.