Continuum photon spectrum from Z^1 Z^1 annihilations in universal extra   dimensions
  We calculate the continuum photon spectrum from the pair annihilation of a Z^1 LKP in non-minimal universal extra dimensions. We find that, due to the preferred annihilation into W^+ W^- pairs, the continuum flux of collinear photons is relatively small compared to the standard case of the B1 as the LKP. This conclusion applies in particular to the spectral endpoint, where also the additional fermionic contributions are not large enough to increase the flux significantly. When searching for the line signal originating from Z^1 Z^1 annihilations, this is actually a perfect situation, since the continuum signal can be regarded as background to the smoking gun signature of a peak in the photon flux at an energy that is nearly equal to the mass of the dark matter particle. This signal, in combination with (probably) a non-observation of the continuum signal at lower photon energies, constitutes a perfect handle to probe the hypothesis of the Z1 LKP being the dominant component of the dark matter observed in the Universe. 
Henrik Melbeus, Alexander Merle, Tommy Ohlsson
hep-ph astro-ph.CO