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 nonthermal 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.
Bibliographical noteFunding Information:
We are grateful to S. Borgani, E. Nardi, E. Pierpaoli, and A. Riotto for useful and lively discussions and to V.S. Berezinsky for interesting comments. In particular, we would like to thank S. Bonometto for pointing out some incorrectness in the first version of this paper. The work of D.M. is supported by an INFN Post-Doc fellowship. This work is partially supported by the EEC TMR network “Beyond the Standard Model”, contract no. FMRX-CT96-0090.
- 98.65. - r