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A<sc>bstract</sc> We argue that the striking similarity between the cosmic abundances of baryons and dark matter, despite their very different astrophysical behavior, strongly motivates the scenario in which dark matter resides within a rich dark sector parallel in structure to that of the standard model. The near cosmic coincidence is then explained by an approximateℤ2exchange symmetry between the two sectors, where dark matter consists of stable dark neutrons, with matter and dark matter asymmetries arising via parallel WIMP baryogenesis mechanisms. Taking a top-down perspective, we point out that an adequateℤ2symmetry necessitates solving the electroweak hierarchy problem in each sector, without our committing to a specific implementation. A higher-dimensional realization in the far UV is presented, in which the hierarchical couplings of the two sectors and the requisiteℤ2-breaking structure arise naturally from extra-dimensional localization and gauge symmetries. We trace the cosmic history, paying attention to potential pitfalls not fully considered in previous literature. Residualℤ2-breaking can very plausibly give rise to the asymmetric reheating of the two sectors, needed to keep the cosmological abundance of relativistic dark particles below tight bounds. We show that, despite the need to keep inter-sector couplings highly suppressed after asymmetric reheating, there can naturally be order-one couplings mediated by TeV scale particles which can allow experimental probes of the dark sector at high energy colliders. Massive mediators can also induce dark matter direct detection signals, but likely at or below the neutrino floor.
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This content will become publicly available on February 1, 2026
Warm Hawking relics from primordialblack hole domination
Abstract We study the cosmological impact of warm, dark-sector relic particles produced as Hawking radiation in a primordial-black-hole-dominated universe before big bang nucleosynthesis. If these dark-sector particles are stable, they would survive to the present day asHawking relicsand modify the growth of cosmological structure. We show that such relics are produced with much larger momenta, but in smaller quantities than the familiar thermal relics considered in standard cosmology. Consequently, Hawking relics with keV–MeV masses affect the growth of large-scale structure in a similar way to eV-scale thermal relics like massive neutrinos. We model their production and evolution, and show that their momentum distributions are broader than comparable relics with thermal distributions. Warm Hawking relics affect the growth of cosmological perturbations and we constrain their abundance to be less than 2% of the dark matter over a broad range of their viable parameter space. Finally, we examine how future measurements of the matter power spectrum can distinguish Hawking relics from thermal particles.
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- PAR ID:
- 10612357
- Publisher / Repository:
- JCAP
- Date Published:
- Journal Name:
- Journal of Cosmology and Astroparticle Physics
- Volume:
- 2025
- Issue:
- 02
- ISSN:
- 1475-7516
- Page Range / eLocation ID:
- 026
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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