  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_\nu=2.75^{+1.28}_{-0.97} eV for halo and 0.26^{+0.20}_{-0.14} eV for
extragalactic (EG) origin.

High Energy Physics - Phenomenology