  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.
