Can Dark Matter be Ultra Heavy Particles ?

The detection of High Energy Cosmic Rays (HECR) with energies around and beyond GZK expected cutoff has introduced the idea of existence of a decaying Ultra Heavy Dark Matter (UHDM). If this type of particles make a substantial part of the CDM, their decay can have important implications for evolution of the large structures and high energy backgrounds. Here we present preliminary results of numerical solution of Boltzmann equations in presence of a decaying CDM. The evolution of baryons and photons energy are calculated. We find that in a homogeneous universe, UHDM can not have a large contribution to the CDM. However, this hypothesis can probably survive if one takes into account the clumsiness of the matter in the Universe.