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Ultra high energy cosmic rays: clustering, GUT scale and neutrino masses

The clustering of ultra high energy (above 5\cdot 10^{19} eV) cosmic rays (UHECR) suggests that they might be emitted by compact sources. We present a statistical analysis on the source density based on the multiplicities. The propagation of UHECR protons is studied in detail. The UHECR spectrum is consistent with the decay of GUT scale particles and/or with the Z-burst. The predicted GUT mass is m_X=10^b GeV, where b=14.6_{-1.7}^{+1.6}. Our neutrino mass prediction depends on the origin of the power part of the spectrum: m_ν=2.75^{+1.28}_{-0.97} eV for halo and 0.26^{+0.20}_{-0.14} eV for extragalactic (EG) origin.