http://arxiv.org/abs/2210.15691
In this Letter, we show that the nonthermal nature of dark matter freeze-in production leads to large, totally correlated dark matter-photon isocurvature perturbations, which are imprinted in anisotropies of the cosmic microwave background (CMB). Isocurvature is typically expected from inflationary physics, but the isocurvature from freeze-in arises post inflation. We compute the freeze-in of millicharged dark matter, generated from electron-positron annihilations in the early Universe. We find that current CMB observations from \textit{Planck} exclude this scenario for dark matter masses between 1 MeV and 10 GeV at more than $2\sigma$, whereas upcoming CMB experiments will have the sensitivity to reach at least the $4\sigma$ level. We anticipate any scenario in which dark matter is nonthermally produced to generically give rise to isocurvature. Our work opens a new avenue for exploring fundamental dark matter physics through its impact on cosmological observables.
N. Bellomo, K. Berghaus and K. Boddy
Mon, 31 Oct 22
38/60
Comments: 8 pages, 3 figures
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