Alexander Kusenko

``Our model [3] makes an interesting prediction for the highest-energy cosmic rays. Just as the protons of the highest energies escape from our Galaxy, they should escape from the host galaxies of remote sources, such as AGNs. Therefore, UHECR with E > 3×10¹⁹ eV should correlate with the extragalactic sources. Moreover, these UHECR should be protons, not heavy nuclei, since the nuclei are trapped in the host galaxies. If and when the data will allow one to determine composition on a case-by-case basis, one can separate E > 3×10¹⁹ eV events into protons and nuclei and observe that the protons correlate with the nearby AGN. This prediction is one of the non-trivial tests of our model: at the highest energies the proton fraction should exist and should correlate with known astrophysical sources.''

Taken from arXiv

Kusensko's prediction depends on the ability of people ``on the ground'' in Argentina to sort protons from heavy nuclei in a case by case basis. If they do, Kusensko's prediction is that only protons come from afar.