Both Warm Dark Matter (WDM) and Cold Dark Matter (CDM) seem to provide plausible explanations for the large-scale structure of the cosmos. But, a little closer to home, simulations of halo galaxies seem to indicate that WDM might better explain smaller scale structures1. This is at odds with the emphasis of particle physicists, who have generally favored CDM as an explanation since current extensions to the Standard Model provide several excellent candidate particles for CDM, such as axions and WIMPs.
1. Cooper, A. P., et al. “A two-point correlation function for Galactic halo stars” Monthly Notices of the Royal Astronomical Society, September 2011. DOI: 10.1111/j.1365-2966.2011.19401.x