PBH dark matter spans all naturalness tiers, with some mechanisms as natural as WIMPs or freeze-in particles, determined by abundance map structure rather than candidate type.
Canonical reference
Axion dark matter from topological defects
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abstract
The cosmological scenario where the Peccei-Quinn symmetry is broken after inflation is investigated. In this scenario, topological defects such as strings and domain walls produce a large number of axions, which contribute to the cold dark matter of the universe. The previous estimations of the cold dark matter abundance are updated and refined based on the field-theoretic simulations with improved grid sizes. The possible uncertainties originated in the numerical calculations are also discussed. It is found that axions can be responsible for the cold dark matter in the mass range $m_a=(0.8-1.3)\times 10^{-4}\mathrm{eV}$ for the models with the domain wall number $N_{\rm DW}=1$, and $m_a\approx\mathcal{O}(10^{-4}-10^{-2})\mathrm{eV}$ with a mild tuning of parameters for the models with $N_{\rm DW}>1$. Such higher mass ranges can be probed in future experimental studies.
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Collapsing Z_N domain walls trap baryons into dense baryoids, yielding a dark matter-baryon energy density ratio of approximately (N-1):1 after the QCD phase transition.
Domain wall annihilation imprints a two-peaked spectrum on induced gravitational waves via an early matter-dominated phase and entropy dilution.
Multi-axion models relax the E/N bound on QCD axion photon coupling and allow subdominant dark matter contribution, but an axion-like particle is typically visible to next-generation experiments.
Models with Peccei-Quinn symmetry and vector-like quarks realize one-loop proton decay through the operator u_R u_R d_R e_R while preserving a residual Z2 that forbids tree-level decay, yielding testable axion-photon couplings and an axion-accompanied decay mode.
In gauged U(1) completions enabling high-quality axion dark matter, cosmic string loops generate a stochastic gravitational wave background with an infrared break frequency that exceeds foregrounds above 10^14 GeV breaking scales and offers a probe at interferometers.
Spontaneous wash-in leptogenesis in Type II Seesaw with Majoron pNGB background enables baryon asymmetry generation alongside dark matter cogenesis for specific v_T, v_sigma and m_j ranges.
A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.
Review classifies QCD axion models extending the standard mass-coupling window and updates bounds from cosmology, astrophysics, and experiments.
citing papers explorer
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Are Primordial Black Holes a Natural Dark Matter Candidate?
PBH dark matter spans all naturalness tiers, with some mechanisms as natural as WIMPs or freeze-in particles, determined by abundance map structure rather than candidate type.
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Baryoid Dark Matter from $\mathbb{Z}_N$ Domain Walls: The $(N-1):1$ origin of the dark matter-baryon coincidence
Collapsing Z_N domain walls trap baryons into dense baryoids, yielding a dark matter-baryon energy density ratio of approximately (N-1):1 after the QCD phase transition.
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Imprint of domain wall annihilation on induced gravitational waves
Domain wall annihilation imprints a two-peaked spectrum on induced gravitational waves via an early matter-dominated phase and entropy dilution.
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How well can the QCD axion hide?
Multi-axion models relax the E/N bound on QCD axion photon coupling and allow subdominant dark matter contribution, but an axion-like particle is typically visible to next-generation experiments.
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One-loop proton decay from Peccei-Quinn symmetry
Models with Peccei-Quinn symmetry and vector-like quarks realize one-loop proton decay through the operator u_R u_R d_R e_R while preserving a residual Z2 that forbids tree-level decay, yielding testable axion-photon couplings and an axion-accompanied decay mode.
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High-Quality Axion Dark Matter at Gravitational Wave Interferometers
In gauged U(1) completions enabling high-quality axion dark matter, cosmic string loops generate a stochastic gravitational wave background with an infrared break frequency that exceeds foregrounds above 10^14 GeV breaking scales and offers a probe at interferometers.
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Type II Seesaw Leptogenesis in a Majoron background
Spontaneous wash-in leptogenesis in Type II Seesaw with Majoron pNGB background enables baryon asymmetry generation alongside dark matter cogenesis for specific v_T, v_sigma and m_j ranges.
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Axions as Dark Matter, Dark Energy, and Dark Radiation
A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.
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The landscape of QCD axion models
Review classifies QCD axion models extending the standard mass-coupling window and updates bounds from cosmology, astrophysics, and experiments.
- Loss of the scaling attractor in self-gravitating domain wall networks
- Specially Embedding a Composite Axion Model