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arXiv · 2605.00103

Pre-inflationary QCD axion stars after moduli domination

Edward Hardy·Noelia Sánchez González·Henry Stubbs·Lorenzo Tranchedone
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Abstract

The growth of adiabatic density perturbations during an era of early matter domination induces $\mathcal{O}(1)$ fluctuations in pre-inflationary QCD axion dark matter across a broad, string-theory-motivated parameter space. Remarkably, at $\Lambda$CDM matter-radiation equality the scale of these perturbations coincides with the quantum Jeans scale, so they collapse to solitonic ``axion stars''. These axion stars have densities up to $10^4\,\mathrm{eV}^4$, and, including their surrounding halos, they contain as much as $50\%$ of dark matter. Direct searches for a smooth axion background can be suppressed, but transient enhancements or indirect astrophysical signals at axion masses $m_a\lesssim 10^{-5}\,{\rm eV}$ would point to a non-standard cosmological history.

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Edward Hardy, Noelia Sánchez González, Henry Stubbs, Lorenzo Tranchedone. 2026-04-30. Pre-inflationary QCD axion stars after moduli domination. https://arxiv.org/abs/2605.00103

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