  The standard CDM model fails to describe the power spectrum of fluctuations
since it gives too much power at small scales. Among other possible
improvements, it has been suggested that an agreement with observations can be
achieved with the addition of a late decaying particle, through the injection
of non-thermal radiation and the consequent increase of the horizon length at
the equivalence time. We analyze the possibility of implementing this idea in
some extensions of the electroweak standard model, discussing the cosmological
and astrophysical bounds to which these schemes are subject.
