Axion-pion thermalization rate in unitarized NLO chiral perturbation theory

Abstract

We compute the axion-pion scattering $a\pi \to \pi \pi$, relevant for the axion thermalization rate in the early universe, within unitarized NLO chiral perturbation theory. The latter extends the range of validity of the chiral expansion of axion-pion scattering and thus provides a crucial ingredient for the reliable determination of the relic density of thermal axions, whenever the axion decoupling temperature is below that of the QCD phase transition. Implications for cosmological observables are briefly discussed.

13 pages, 12 figures. Typos corrected and slightly changed results. Extended discussion and appendix added

References in corpus (12)

• The QCD transition temperature: results with physical masses in the continuum limit
• FLAG Review 2021
• The pion-pion scattering amplitude. IV: Improved analysis with once subtracted Roy-like equations up to 1100 MeV
• Identification of a Scalar Glueball
• Thermal axion production in the primordial quark-gluon plasma
• An even lighter QCD axion
• Dark matter from an even lighter QCD axion: trapped misalignment
• Cosmological Bound on the QCD Axion Mass, Redux
• Thermal axion production at low temperatures: a smooth treatment of the QCD phase transition
• Thermal QCD Axions across Thresholds
• Novel cosmological bounds on thermally-produced axion-like particles
• Breakdown of chiral perturbation theory for the axion hot dark matter bound

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• Catalogues of Cosmologically Self-Consistent Hadronic QCD Axion Models
• Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments