  Spin and charge-current dynamics after ultrafast spin-polarized excitation in
a normal metal are studied theoretically using a wave-diffusion theory. It is
shown analytically how this macroscopic approach correctly describes the
ballistic and diffusive properties of spin and charge transport, but also
applies to the intermediate regime between these two limits. Using the
wave-diffusion equations we numerically analyze spin and charge dynamics after
ultrafast excitation of spin polarized carriers in thin gold films. Assuming
slightly spin-dependent momentum relaxation times, we find that a unified
treatment of diffusive and ballistic transport yields robust signatures in the
spin and charge dynamics, which are in qualitative agreement with recent
experimental results [Phys. Rev. Lett 107, 076601 (2011)]. The influence of
boundary effects on the temporal signatures of spin transport is also studied.
