http://arxiv.org/abs/1701.08750
Light dark matter is a compelling experimental target in light of stringent constraints on heavier WIMPs. However, for a sub-MeV WIMP, the universe is sufficiently well understood at temperature below 10 MeV that there is no room for it to be a thermal relic. Avoiding thermalization is itself a strong constraint with significant implications for direct detection. In this paper, we explore the space of models of sub-MeV dark matter with viable cosmologies. The parameter space of these models that is also consistent with astrophysical and lab-based limits is highly restricted for couplings to electrons but somewhat less constrained for nuclei. We find that achieving nuclear cross-sections above the neutrino floor necessarily predicts a new contribution to the effective number of neutrino species, $\Delta N_{\rm eff} = 0.09$ that will be tested by the next generation of CMB observations. On the other hand, models with absorptions signatures of dark matter are less restricted by cosmology even with future observations.
D. Green and S. Rajendran
Tue, 31 Jan 17
24/58
Comments: 24 pages, 5 figures
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