O(g) plasma effects in jet quenching

Abstract

We consider the bremsstrahlung energy loss of high energy partons moving in the quark-gluon plasma, at weak coupling. We show that the rates for these processes receive large O(g) corrections from classical (nonabelian) plasma physics effects, which are calculated. In the high-energy (deep LPM) regime these corrections can be absorbed in a change of the transverse momentum broadening coefficient $\hat{q}$, which we give to the next-to-leading order. The correction is large even at relatively weak couplings $\alpha_s\sim 0.1$, as is typically found for such effects, signaling difficulties with the perturbative expansion. Our approach is based on an effective "Euclideanization" property of classical physics near the light-cone, which allows an effective theory approach based on dimensional reduction and suggests a new possibility for the nonperturbative lattice study of these effects.