  The annihilation of non-relativistic dark matter particles at tree level can
be strongly enhanced by the radiation of an additional gauge boson. This is
particularly true for the helicity-suppressed annihilation of Majorana
particles, like neutralinos, into fermion pairs. Surprisingly, and despite the
potentially large effect due to the strong coupling, this has so far been
studied in much less detail for the internal bremsstrahlung of gluons than for
photons or electroweak gauge bosons. Here, we aim at bridging that gap by
presenting a general analysis of neutralino annihilation into quark anti-quark
pairs and a gluon, allowing e.g. for arbitrary neutralino compositions and
keeping the leading quark mass dependence at all stages in the calculation. We
find in some cases largely enhanced annihilation rates, especially for
scenarios with squarks being close to degenerate in mass with the lightest
neutralino, but also notable distortions in the associated antiproton and
gamma-ray spectra. Both effects significantly impact limits from indirect
searches for dark matter and are thus important to be taken into account in,
e.g., global scans. For extensive scans, on the other hand, full calculations
of QCD corrections are numerically typically too expensive to perform for each
point in parameter space. We present here for the first time an efficient,
numerically fast implementation of QCD corrections, extendable in a
straight-forward way to non-supersymmetric models, which avoids computationally
demanding full one-loop calculations or event generator runs and yet fully
captures the leading effects relevant for indirect dark matter searches. In
this context, we also present updated constraints on dark matter annihilation
from cosmic-ray antiproton data. Finally, we comment on the impact of our
results on relic density calculations.
