Vernon Barger, Wai-Yee Keung, Danny Marfatia
We show that the energy spectra from dark matter (DM) annihilation into
$f^+f^-\gamma$ (where $f$ is a light fermion) via chirality preserving
interactions are identical in 3 scenarios: (a) DM is a Majorana fermion and the
particle exchanged is a scalar, (b) DM is a Majorana fermion and the particle
exchanged is a vector and (c) DM is a scalar and the particle exchanged is a
fermion. For cases (a) and (c), we also calculate the differential cross
section to $\ell^+f^-V$, where $V=W,Z,\gamma$, and $\ell$ is a light fermion
that may or not be the same as $f$. The form of the cross section depends on
whether the DM is a Majorana fermion or a scalar but in both cases its form is
independent of $V$.
View original:
http://arxiv.org/abs/1111.4523
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