Non-Thermal Production of WIMPs and the Sub-Galactic Structure of the Universe

Abstract

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.

Figures (2)

• Figure 1: Comparison of the power spectra of the CDM model(long dashed curve), the WDM model with $m_W=1$keV(short dashed curve) and the NTDM model with $r_c=1.5\times 10^{-7}$ (solid curve).
• Figure 2: The power spectra of the CDM model (long dashed curve), the WDM model with $m_W=750$eV (short dashed curve) and the NTDM models with $r_c=(1.3,1.4,1.5)\times 10^{-7}$ (solid curves, from top down), compared to the observed lyman-$\alpha$$P(k)$ at $z=2.5$ (filled circles with error bars).