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Bounds on Dark-Matter Annihilations from 21-cm Data.

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The 21-cm absorption feature at redshift z≈17 constrains dark-matter (DM) annihilations. These new bounds on DM annihilation cross sections are as strong as existing limits from other methods.

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Area of Science:

  • Cosmology
  • Astrophysics
  • Particle Physics

Background:

  • The 21-cm line is a crucial probe of the early universe, sensitive to the thermal history of the intergalactic medium.
  • Dark-matter (DM) annihilation in the early universe can inject energy into the intergalactic medium, affecting its temperature.
  • Previous studies have used various astrophysical observations to constrain dark-matter properties.

Purpose of the Study:

  • To investigate the implications of the observed 21-cm absorption feature at redshift z≈17 for dark-matter annihilation.
  • To derive new constraints on dark-matter annihilation cross sections across a range of dark-matter masses.
  • To compare these new constraints with existing limits from other observational probes.

Main Methods:

  • Analyzing the 21-cm absorption spectrum observed at redshift z≈17.
  • Modeling the energy injection into the intergalactic medium from dark-matter annihilation.
  • Calculating the impact of this energy injection on the intergalactic medium's temperature.
  • Establishing bounds on dark-matter annihilation cross sections by requiring the absence of significant heating that would erase the observed absorption feature.

Main Results:

  • The observation of the 21-cm absorption feature at z≈17 implies significant constraints on dark-matter annihilation.
  • These constraints apply to a broad range of dark-matter masses.
  • The derived bounds on dark-matter annihilation cross sections are competitive with, and comparable to, the strongest limits from all other existing observables.

Conclusions:

  • The 21-cm absorption feature provides a powerful new probe for constraining dark-matter properties.
  • These findings significantly advance our understanding of dark-matter annihilation and its cosmological impact.
  • Future observations of the 21-cm signal can further refine these dark-matter constraints.