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{sup 3}{mu}, while the damping rates of other particles are of order e{sup 4}{mu} or e{sup 4}{mu}thinsp 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. {copyright} {ital 1997} {ital The American Physical Society}