Tighter limits on dark matter explanations of the anomalous EDGES 21 cm signal

By E. Kovetz, V. Poulin, V. Gluscevic, K. Boddy, R. Barkana, M. Kamionkowski. Physical Review D, 2018

140 citations recorded by the source corpus.

We investigate the hypothesis that Coulomb-type interactions between dark matter (DM) and baryons explain the anomalously low 21cm brightness-temperature minimum at redshift z ~ 17 that was recently measured by the EDGES experiment. In particular, we reassess the validity of the scenario where a small fraction of the total DM is millicharged, focusing on newly derived constraints from Planck 2015 cosmic microwave background (CMB) data. Crucially, the CMB power spectrum is sensitive to DM-baryon scattering if the fraction of interacting DM is larger than (or comparable to) the fractional uncertainty in the baryon energy density. Meanwhile, there is a mass-dependent lower limit on the fraction for which the required interaction to cool the baryons sufficiently is so strong that it drives the interacting-DM temperature to the baryon temperature prior to their decoupling from the CMB. If this occurs as early as recombination, the cooling saturates. We precisely determine the viable parameter space for millicharged DM, and find that only a fraction (m_chi/MeV) 0.0115% <~ f <~ 0.4% of the entire DM content, and only for DM-particle masses between 0.5 MeV - 35 MeV, can be charged at the level needed to marginally explain the anomaly, without violating limits from SLAC, CMB, Big-Bang nucleosynthesis (BBN), or stellar and SN1987A cooling. In reality, though, we demonstrate that at least moderate fine tuning is required to both agree with the measured absorption profile and overcome various astrophysical sources of heating. Finally, we point out that a ~0.4% millicharged DM component which is tightly coupled to the baryons at recombination may resolve the current 2-sigma tension between the BBN and CMB determinations of the baryon energy density. Future CMB-S4 measurements will be able to probe this scenario directly.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/eba76e1d4ade4ef4d22ccaff55de7fa051b81b45

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Citations in the corpus

Physics beyond colliders at CERN: beyond the Standard Model working group report (2019, background): “Data from [238], interpretation from [241].”
Direct detection of strongly interacting sub-GeV dark matter via electron recoils (2019, background): “DM abundance [70]; for comparison, we show the CMB constraint for a fractional abundance of f ˜ = 1% (blue line, “CMB (f ˜ = 1%)”), in which case the entire region at high cross section is disfavored [114]. For the N e constraints from the CMB and BBN, we assume that the dark gauge coupling is sufﬁc”
The Dark Photon (2020, background): “Milli-charged particles as dark matter have been proposed (Kovetz et al., 2018) to explain the anomalous 21 cm hydrogen absorption signal reported by the EDGES Experiment (Monsalve et al., 2018).”
PICO: Probe of Inflation and Cosmic Origins (2019, methodology): “This effect has been used to search for evidence of dark-matter–proton scattering over a range of masses, couplings, and interaction models [55–62], to test the possibility of an interacting dark-matter sub-component [61], and to provide consistency tests of dark matter in the context of the anomalo”
CMB-S4 Science Case, Reference Design, and Project Plan (2019, unknown): “[285, 281].”