  We present a lattice study of the momentum broadening experienced by a hard
parton in the quark-gluon plasma. In particular, the contributions to this
real-time phenomenon from soft modes are extracted from a set of
gauge-invariant operators in a dimensionally reduced effective theory
(electrostatic QCD), which can be simulated on a Euclidean lattice. At the
temperatures accessible to present experiments, the soft contributions to the
jet quenching parameter are found to be quite large. We compare our results to
phenomenological models and to holographic computations.
