Damping rates of hard momentum particles in a cold ultrarelativistic plasma

We compute the damping rates of one-particle excitations in a cold ultrarelativistic plasma to leading order in the coupling constant e for three types of interaction: Yukawa coupling to a massless scalar boson, QED, and QCD. Damping rates of charged particles in QED and QCD are of order e(3) mu, while the damping rates of other particles are of order e(4) mu or e(4) mu log(1/e). We find that the damping rate of an electron or of a quark is constant far from the Fermi surface, and decreases linearly with the excitation energy close to the Fermi surface. This unusual behavior is attributed to the long-range magnetic interactions.