21 cm limits on decaying dark matter and primordial black holes
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© 2018 American Physical Society. Recently the Experiment to Detect the Global Epoch of Reionization Signature reported the detection of a 21 cm absorption signal stronger than astrophysical expectations. In this paper we study the impact of radiation from dark matter (DM) decay and primordial black holes (PBHs) on the 21 cm radiation temperature in the reionization epoch, and impose a constraint on the decaying dark matter and PBH energy injection in the intergalactic medium, which can heat up neutral hydrogen gas and weaken the 21 cm absorption signal. We assume a strong coupling limit in the Lyman-α background and consider decay channels DM→e+e-,γγ, μ+μ-, τ+τ-, bb and the 1015-17 g mass range for primordial black holes, and require that the heating of the neutral hydrogen does not negate the 21 cm absorption signal. For e+e-, γγ final states and PBH cases we find strong 21 cm bounds that can be more stringent than the current extragalactic diffuse photon bounds. For the DM→e+e- channel, the lifetime bound is τDM>1027 s for sub-GeV dark matter. The bound is τDM≥1026 s for the sub-GeV DM→γγ channel and reaches 1027 s for MeV DM. For bb and μ+μ- cases, the 21 cm constraint is better than all the existing constraints for mDM<30 GeV where the bound on τDM≥1026 s. For both DM decay and primordial black hole cases, the 21 cm bounds significantly improve over the cosmic microwave background damping limits from Planck data.
author list (cited authors)
Clark, S. J., Dutta, B., Gao, Y. u., Ma, Y., & Strigari, L. E
complete list of authors
Clark, Steven J||Dutta, Bhaskar||Gao, Yu||Ma, Yin-Zhe||Strigari, Louis E