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Abstract In this work, we study the cosmological effects of a tower of warm dark matter states on the cosmic microwave background (CMB) and on large-scale structure (LSS). For concreteness, we consider the Nnaturalness model, which is a proposed mechanism to solve the Higgs hierarchy problem. In this framework, the sector of particles of the Standard Model is copiedNtimes where the Higgs mass-squared value is the only parameter that changes between sectors. The other sectors are similar to our own, except their particles are proportionally heavier and cooler compared to the Standard Model sector. Since each sector is extremely weakly coupled to other sectors, direct observations of the new particles are not expected. The addition of new photon-like species and new neutrino-like species, however, can be detected through the CMB and in LSS data. These additional neutrinos form a tower of states with increasing mass and decreasing temperature compared to the SM neutrinos. This tower causes a more gradual suppression of the matter power spectrum across different comoving wavenumbers than a single warm dark matter state would. We quantitatively explore these effects in theNnaturalness model and compute the parameter space allowed by the Planck 2018, weak lensing, and Lyman-α datasets. Depending on the underlying parameters, Planck 2018 and weak lensing data can requireNnaturalness to be tuned at the 10% level for Dirac neutrinos and at the 5% level for Majorana neutrinos. The additional neutrino states are crucial in constraining the model, particularly through their suppression of the power spectrum at small scales. The inclusion of many warm dark matter species is computationally very challenging and we make detailed assessments of our approximations and comment on potential future improvements.
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Dark Radiation from Neutrino Mixing after Big Bang Nucleosynthesis
Light dark fermions can mass mix with the standard model (SM) neutrinos. As a result, through oscillations and scattering, they can equilibrate in the early universe. Interactions of the dark fermion generically suppress such production at high temperatures but enhance it at later times. We find that for a wide range of mixing angles and interaction strengths equilibration with SM neutrinos occurs at temperatures near the dark fermion mass. For masses below an MeV, this naturally occurs after nucleosynthesis and opens the door to a variety of dark sector dynamics with observable imprints on the CMB and large scale structure, and with potential relevance to the tensions in H0 and S8.
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- PAR ID:
- 10523419
- Publisher / Repository:
- American Physical Society
- Date Published:
- Journal Name:
- Physical Review Letters
- Volume:
- 131
- Issue:
- 22
- ISSN:
- 0031-9007
- Subject(s) / Keyword(s):
- cosmology dark radiation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/PhysRevLett.131.221001
