Gamma Rays from Kaluza-Klein Dark Matter

A TeV $\gamma$-ray signal from the direction of the Galactic center (GC) has been detected by the High Energy Stereoscopic System (H.E.S.S.) experiment. The origin of this signal, however, is unknown. In this letter we investigate whether dark matter annihilating near the center can be the explanation. We calculate the continuous $\gamma$-ray spectrum from Kaluza-Klein dark matter annihilations, since these among other channels contain extremely high energy leptons. We find that the subsequent decays of $\tau$ leptons will be important for this type of models. Moreover, we find a radiative cross section from the primary leptons which has an important tail up to high energies. This gives a nice signature of the expected $\gamma$-ray spectrum, an almost flat energy distribution which drops abruptly at the dark matter particle mass. For a mass of about 1 TeV, and taking into account current N-body simulation halo profiles, with an enhancement due to adiabatic compression caused by the stellar cluster near the GC, the resulting spectrum gives a good fit to a large range of the H.E.S.S. data. Explaining the complete range of data would, however, require masses larger than around 4 TeV, which is disfavored for the particular model considered here. A model where the gauge coupling is twice as large would give the correct relic density and a well fitting photon spectrum for a particle mass of roughly 10 TeV.