  We compute the electromagnetic radiative corrections to all leading
annihilation processes which may occur in the Galactic dark matter halo, for
dark matter in the framework of supersymmetric extensions of the Standard Model
(MSSM and mSUGRA), and present the results of scans over the parameter space
that is consistent with present observational bounds on the dark matter density
of the Universe. Although these processes have previously been considered in
some special cases by various authors, our new general analysis shows novel
interesting results with large corrections that may be of importance, e.g., for
searches at the soon to be launched GLAST gamma-ray space telescope. In
particular, it is pointed out that regions of parameter space where there is a
near degeneracy between the dark matter neutralino and the tau sleptons,
radiative corrections may boost the gamma-ray yield by up to three or four
orders of magnitude, even for neutralino masses considerably below the TeV
scale, and will enhance the very characteristic signature of dark matter
annihilations, namely a sharp step at the mass of the dark matter particle.
Since this is a particularly interesting region for more constrained mSUGRA
models of supersymmetry, we use an extensive scan over this parameter space to
verify the significance of our findings. We also re-visit the direct
annihilation of neutralinos into photons and point out that, for a considerable
part of the parameter space, internal bremsstrahlung is more important for
indirect dark matter searches than line signals.
