Majumder, A; Müller, B; Mrówczyński, S, *Momentum broadening of a fast parton in a perturbative quark-gluon plasma*,
Physical Review D - Particles, Fields, Gravitation, and Cosmology, vol. 80 no. 12
(2009),
pp. 125020 [repository], [doi] .
**Abstract:**

*The average transverse momentum transfer per unit path length to a fast parton scattering elastically in a perturbative quark-gluon plasma is related to the radiative energy loss of the parton. We first calculate the momentum transfer coefficient q^ in terms of a classical Langevin problem and then define it quantum mechanically through a scattering matrix element. After treating the well-known case of a quark-gluon plasma in equilibrium, we consider an off-equilibrium unstable plasma. As a specific example, we treat the two-stream plasma with unstable modes of longitudinal chromoelectric field. In the presence of the instabilities, q^ is shown to exponentially grow in time. © 2009 The American Physical Society.*