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)=${\mathit{cg}}^2$ ln(1/g)T+O(${\mathit{g}}^2$T) 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(${\mathit{g}}^2$T) contributon is incalculable in perturbation theory without further assumptions. For QCD with ${\mathit{N}}_{\mathit{c}}$ colors we find ${\mathit{c}}_{\mathit{g}}$=+${\mathit{N}}_{\mathit{c}}$/4π for gluons and ${\mathit{c}}_{\mathit{q}}$=+(${\mathit{N}}_{\mathit{c}}^2$-1)/8π${\mathit{N}}_{\mathit{c}}$ 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.