  Stable particle dark matter may well originate during the decay of long-lived
relic particles, as recently extensively examined in the cases of the axino,
gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that
in much of the viable parameter space such dark matter emerges naturally
warm/hot or mixed. In particular, decay produced gravitinos (KK-gravitons) may
only be considered cold for the mass of the decaying particle in the several
TeV range, unless the decaying particle and the dark matter particle are almost
degenerate. Such dark matter candidates are thus subject to a host of
cosmological constraints on warm and mixed dark matter, such as limits from a
proper reionisation of the Universe, the Lyman-alpha forest, and the abundance
of clusters of galaxies.. It is shown that constraints from an early
reionsation epoch, such as indicated by recent observations, may potentially
limit such warm/hot components to contribute only a very small fraction to the
dark matter.
