  At finite temperature and chemical potential, the leading-order
(hard-thermal-loop) contributions to the gauge-boson propagator lead to
momentum-dependent thermal masses for propagating quasiparticles as well as
dynamical screening and Landau damping effects. We compare the
hard-thermal-loop propagator with the complete large-N_f gluon propagator, for
which the usually subleading contributions, such as a finite width of
quasiparticles, can be studied at nonperturbatively large effective coupling.
We also study quantitatively the effect of Friedel oscillations in
low-temperature electrostatic screening.
