Ultra High Energy Gamma Rays as signature of Topological Defects

We argue that due to various restrictions only necklaces and monopolonia survive as potential sources of ultra-high energy cosmic rays, among the topological defects studied so far. Other promising sources which are similar to topological defects are relic superheavy particles. All these sources have an excess of pions (and thus photons) over nucleons at production. We demonstrate that in the case of necklaces the diffuse proton flux can be larger than photon flux, while monopolonia and relic particles are concentrated in the Galactic halo, and the photon flux dominates. In all cases considered so far, including necklaces, photons must be present in ultra-high energy radiation