The cosmology of sub-MeV dark matter

• Published in: The journal of high energy physics 2017-10, Vol.2017 (10), p.1-28, Article 13
• Main Authors: Green, Daniel, Rajendran, Surjeet
• Format: Article
• Language: English
• Subjects: Astronomical models; Beyond Standard Model; Classical and Quantum Gravitation; Cosmology; Cosmology of Theories beyond the SM; Couplings; Dark matter; Elementary Particles; High energy physics; Nuclear cross sections; Nuclei (nuclear physics); Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; String Theory; Thermalization (energy absorption); Universe; Weakly interacting massive particles
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP10(2017)013

A bstract 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 temperatures 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. We discuss several representative models chosen to have large cross-sections in direct detection experiments. 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 well-above the neutrino floor necessarily predicts a new contribution to the effective number of neutrino species, Δ N eff = 0 . 09 that will be tested by the next generation of CMB observations. On the other hand, models with absorption signatures of dark matter are less restricted by cosmology even with future observations.