Abstract
We derive the spectra arising from non-relativistic dark matter annihilations or decays into intermediary particles with arbitrary spin, which subsequently produce neutrinos or photons via two-body decays. Our approach is model independent and predicts spectral features restricted to a kinematic box. The overall shape within that box is a polynomial determined by the polarization of the decaying particle. We illustrate our findings with two examples. First, with the neutrino spectra arising from dark matter annihilations into the massive Standard Model gauge bosons. Second, with the gamma-ray and neutrino spectra generated by dark matter annihilations into hypothetical massive spin-2 particles. Our results are in particular applicable to the 750 GeV diphoton excess observed at the LHC if interpreted as a spin-0 or spin-2 particle coupled to dark matter. We also derive limits on the dark matter annihilation cross section into this resonance from the non-observation of the associated gamma-ray spectral features by the H.E.S.S. telescope.
Highlights
We derive the spectra arising from non-relativistic dark matter annihilations or decays into intermediary particles with arbitrary spin, which subsequently produce neutrinos or photons via two-body decays
Our results are in particular applicable to the 750 GeV diphoton excess observed at the LHC if interpreted as a spin-0 or spin-2 particle coupled to dark matter
In order to account for the finite detector resolution, the spectra are convoluted with a Gaussian distribution of 15% of the energy, a value which is at reach of current gamma-ray and neutrino telescopes [71, 72]
Summary
We start off with a simple example to illustrate the concepts and familiarize ourselves with the notation. If either the production or the decay is unpolarized, the polynomial feature disappears and we obtain a flat-box shape, as in the case of a scalar mediator [9]. We show this quantity in figure 3 for the three cases of transverse W +. The same is true for Z → ννup to factors of two if the Z is produced in pairs This concludes our example and shows that the polarization of intermediate particles in DM annihilation generically plays a role for the resulting spectra
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