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Light dark matter and dark radiation

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Abstract

Light (M ≤ 20 MeV) dark-matter particles freeze out after neutrino decoupling. If the dark-matter particle couples to a neutrino or an electromagnetic plasma, the late time entropy production from dark-matter annihilation can change the neutrino-to-photon temperature ratio, and equally the effective number of neutrinos N eff. We study the non-equilibrium effects of dark-matter annihilation on the N eff and the effects by using a thermal equilibrium approximation. Both results are constrained with Planck observations. We demonstrate that the lower bounds of the dark-matter mass and the possibilities of the existence of additional radiation particles are more strongly constrained for dark-matter annihilation process in non-equilibrium.

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Authors and Affiliations

  1. Department of Physics and IPAP, Yonsei University, Seoul, 03722, Korea

    Jae Ho Heo & C. S. Kim

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  1. Jae Ho Heo
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  2. C. S. Kim
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Correspondence to Jae Ho Heo.

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Heo, J.H., Kim, C.S. Light dark matter and dark radiation. Journal of the Korean Physical Society 68, 715–721 (2016). https://doi.org/10.3938/jkps.68.715

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