Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.
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Cosmological window onto the string axiverse and the supersymmetry breaking scale
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abstract
In the simplest picture, the masses of string axions populating the axiverse depend on two parameters: the supersymmetry breaking scale $M_{\rm susy}$ and the action $S$ of the string instantons responsible for breaking the axion shift symmetry. In this work, we explore whether cosmological data can be used to probe these two parameters. Adopting string-inspired flat priors on $\log_{10}M_{\rm susy}$ and $S$, and imposing that $M_{\rm susy}$ be sub-Planckian, we find $S=198\pm28$. These bounds suggest that cosmological data complemented with string-inspired priors select a quite narrow axion mass range within the axiverse, $\log_{10}(m_a/{\rm eV}) = -21.5^{+1.3}_{-2.3}$. We find that $M_{\rm susy}$ remains unconstrained due to a fundamental parameter degeneracy with $S$. We explore the significant impact of other choices of priors on the results, and we comment on similar findings in recent previous literature.
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QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.
A barotropic fluid with ω_s ≈ 0.29 and Ω_s ≈ 1.5×10^{-5} raises the inferred H0 to match SH0ES while remaining consistent with Planck CMB, DESI BAO, and Pantheon data.
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.
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.
citing papers explorer
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Double the axions, half the tension: multi-field early dark energy eases the Hubble tension
Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.
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Constraining F-theory Model Building with QCD Axions
QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.
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A barotropic alternative to Early Dark Energy for alleviating the $H_0$ tension
A barotropic fluid with ω_s ≈ 0.29 and Ω_s ≈ 1.5×10^{-5} raises the inferred H0 to match SH0ES while remaining consistent with Planck CMB, DESI BAO, and Pantheon data.
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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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In the Realm of the Hubble tension $-$ a Review of Solutions
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.