  The standard model of GRB afterglows assumes that the radiation observed as a
delayed emission is of synchrotron origin, which requires the shock magnetic
field to be relatively homogeneous on small scales. An alternative mechanism --
jitter radiation, which traditionally has been applied to the prompt emission
-- substitutes synchrotron when the magnetic field is tangled on a microscopic
scale. Such fields are produced at relativistic shocks by the Weibel
instability. Here we explore the possibility that small-scale fields populate
afterglow shocks. We derive the spectrum of jitter radiation under the
afterglow conditions. We also derive the afterglow lightcurves for the ISM and
Wind profiles of the ambient density. Jitter self-absorption is calculated here
for the first time. We find that jitter radiation can produce afterglows
similar to synchrotron-generated ones, but with some important differences. We
compare the predictions of the two emission mechanisms. By fitting
observational data to the synchrotron and jitter afterglow lightcurves, it can
be possible to discriminate between the small-scale vs large-scale magnetic
field models in afterglow shocks.
