There is increasing evidence that conventional cold dark matter (CDM) models
lead to conflicts between observations and numerical simulations of dark matter
halos on sub-galactic scales. Spergel and Steinhardt showed that if the CDM is
strongly self-interacting, then the conflicts disappear. However, the
assumption of strong self-interaction would rule out the favored candidates for
CDM, namely weakly interacting massive particles (WIMPs), such as the
neutralino. In this paper we propose a mechanism of non-thermal production of
WIMPs and study its implications on the power spectrum. We find that the
non-vanishing velocity of the WIMPs suppresses the power spectrum on small
scales compared to what it obtained in the conventional CDM model. Our results
show that, in this context, WIMPs as candidates for dark matter can work well
both on large scales and on sub-galactic scales.Comment: 6 pages, 2 figures; typo corrected; to appear in PR
