  The decay of current autocorrelation functions is investigated for quantum
systems featuring strong 'interactions'. Here, the term interaction refers to
that part of the Hamiltonian causing the (major) decay of the current. On the
time scale before the (first) zero-crossing of the current, its relaxation is
shown to be well described by a suitable perturbation theory in the lowest
orders of the interaction strength, even and especially if interactions are
strong. In this description the relaxation is found to be rather close to a
Gaussian decay and the resulting diffusion coefficient approximately scales
with the inverse interaction strength. These findings are also confirmed by
numerical results from exact diagonalization for several one-dimensional
transport models including spin transport in the Heisenberg chain w.r.t.
different spin quantum numbers, anisotropy, next-to-nearest-neighbor
interaction, or alternating magnetic field; energy transport in the Ising chain
with tilted magnetic field; and transport of excitations in a randomly coupled
modular quantum system. The impact of these results for weak interactions is
finally discussed.
