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| Main Authors: | , , , |
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| Format: | Preprint |
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2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2601.08221 |
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| _version_ | 1866918486557589504 |
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| author | Bouzoud, Killian Ghiglieri, Jacopo Laine, M. Sakoda, G. S. S. |
| author_facet | Bouzoud, Killian Ghiglieri, Jacopo Laine, M. Sakoda, G. S. S. |
| contents | Axions coupled to thermal non-Abelian gauge fields may have cosmological significance. As the heat bath defines a frame, its influence depends separately on energy and momentum. A light-like momentum ($k \approx ω$) is relevant for the axion contribution to the effective number of light neutrinos, $ΔN^{ }_\mathrm{eff}$, whereas a vanishing momentum ($k=0$) plays a role for warm natural inflation or ultralight dark matter, and has been employed in lattice estimates (both classical and quantum-statistical) of the strong sphaleron rate. Focussing on soft energies ($α_\mathrm{s}^{ }T \ll ω\ll πT$), we carry out an HTL computation to show how the domains $k=0$ and $k \approx ω$ interpolate to each other. We then compare with lattice data at $k=0$, and connect our analysis to NLO computations at $k \approx ω\ge πT$. Assembling the current best input, we re-investigate light QCD axion decoupling dynamics at $T \ge 200$ MeV, showing that efficient interactions in the ultrasoft domain increase $ΔN^{ }_\mathrm{eff}$ from $\sim 0.03$ to $\sim 0.04$ at $f^{ }_a = 4\times 10^8_{ }$ GeV. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_08221 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Energy and momentum dependence of the soft-axion interaction rate Bouzoud, Killian Ghiglieri, Jacopo Laine, M. Sakoda, G. S. S. High Energy Physics - Phenomenology Axions coupled to thermal non-Abelian gauge fields may have cosmological significance. As the heat bath defines a frame, its influence depends separately on energy and momentum. A light-like momentum ($k \approx ω$) is relevant for the axion contribution to the effective number of light neutrinos, $ΔN^{ }_\mathrm{eff}$, whereas a vanishing momentum ($k=0$) plays a role for warm natural inflation or ultralight dark matter, and has been employed in lattice estimates (both classical and quantum-statistical) of the strong sphaleron rate. Focussing on soft energies ($α_\mathrm{s}^{ }T \ll ω\ll πT$), we carry out an HTL computation to show how the domains $k=0$ and $k \approx ω$ interpolate to each other. We then compare with lattice data at $k=0$, and connect our analysis to NLO computations at $k \approx ω\ge πT$. Assembling the current best input, we re-investigate light QCD axion decoupling dynamics at $T \ge 200$ MeV, showing that efficient interactions in the ultrasoft domain increase $ΔN^{ }_\mathrm{eff}$ from $\sim 0.03$ to $\sim 0.04$ at $f^{ }_a = 4\times 10^8_{ }$ GeV. |
| title | Energy and momentum dependence of the soft-axion interaction rate |
| topic | High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2601.08221 |