  Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.
