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Universal lower bound on the axion decay constant from free streaming effects

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arxiv 2507.01956 v1 pith:TIAPDCI4 submitted 2025-07-02 astro-ph.CO hep-ph

classification astro-ph.COhep-ph
keywords axionboundmodelsuniversalabundanceconstantconstraintsdecay
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

We show that enhancement of the axion relic abundance compared to the standard misalignment contribution generically leads to the production of nonzero momentum axion modes, resulting in warm dark matter behavior and enhanced isocurvature perturbations. It leads to universal constraints on the axion parameter space that are independent of detailed model assumptions and cosmological history. For models enhancing relic abundance with gradient axion modes, observations of the Lyman-$\alpha$ forest impose a lower bound on the axion decay constant, $f_a \gtrsim 10^{15} {\rm GeV}\,(10^{-18}{\rm eV}/m_a)$, from the free-streaming effect. For models relying on the delay of coherent axion oscillations, we obtain a slightly weaker bound, $f_a \gtrsim 10^{14} {\rm GeV}\,(10^{-18}{\rm eV}/m_a)$. We make relatively conservative choices to establish these universal bounds but also provide scaling parameters that can be calibrated for stronger constraints in concrete models and updated as observations improve.

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Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Dark Matter and Baryon Asymmetry from Monopole-Axion Interactions

    hep-ph 2025-11 conditional novelty 8.0 of 10

    A rotating QCD axion dissipates kinetic energy via dark monopole dyon transitions, explaining dark matter and baryon asymmetry with a predicted axion decay constant below 10^9 GeV.

  2. Growth of Structure in Multi-species Wave Dark Matter

    astro-ph.CO 2025-10 unverdicted novelty 7.0 of 10

    Derives the power spectrum evolution and cross-spectra for arbitrary multi-species wave and particle dark matter, incorporating free-streaming, Jeans scales, and intrinsic fluctuations.

  3. Multi-species Dark Matter with Warmth and Randomness

    astro-ph.CO 2025-10 unverdicted novelty 7.0 of 10

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  4. Echoes of Global Cosmic Strings

    hep-ph 2026-04 unverdicted novelty 4.0 of 10

    Global cosmic strings from symmetry breaking produce Nambu-Goldstone bosons whose cosmological signatures can be constrained by current and upcoming CMB and large-scale structure observations.

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