dorsal/arxiv
View SchemaEnergy and momentum dependence of the soft-axion interaction rate
| Authors | Killian Bouzoud, Jacopo Ghiglieri, M. Laine, G. S. S. Sakoda |
|---|---|
| Categories | |
| ArXiv ID | 2601.08221vv1 |
| URL | https://arxiv.org/abs/2601.08221 |
| License | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
Abstract
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 ($k \approx \omega$) is relevant for the axion contribution to the effective number of light neutrinos, $\Delta N^{ }_\mathrm{eff}$, 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 ($\alpha_\mathrm{s}^{ }T \ll \omega \ll \pi T$), we carry out an HTL computation to show how the domains $k=0$ and $k \approx \omega$ interpolate to each other. We then compare with lattice data at $k=0$, and connect our analysis to NLO computations at $k \approx \omega \ge \pi T$. 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 $\Delta N^{ }_\mathrm{eff}$ from $\sim 0.03$ to $\sim 0.04$ at $f^{ }_a = 4\times 10^8_{ }$ GeV.
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"abstract": "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 ($k \\approx \\omega$) is relevant for the axion contribution to the effective number of light neutrinos, $\\Delta N^{ }_\\mathrm{eff}$, 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 ($\\alpha_\\mathrm{s}^{ }T \\ll \\omega \\ll \\pi T$), we carry out an HTL computation to show how the domains $k=0$ and $k \\approx \\omega$ interpolate to each other. We then compare with lattice data at $k=0$, and connect our analysis to NLO computations at $k \\approx \\omega \\ge \\pi T$. 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 $\\Delta N^{ }_\\mathrm{eff}$ from $\\sim 0.03$ to $\\sim 0.04$ at $f^{ }_a = 4\\times 10^8_{ }$ GeV.",
"arxiv_id": "2601.08221",
"authors": [
"Killian Bouzoud",
"Jacopo Ghiglieri",
"M. Laine",
"G. S. S. Sakoda"
],
"categories": [
"hep-ph"
],
"license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
"title": "Energy and momentum dependence of the soft-axion interaction rate",
"url": "https://arxiv.org/abs/2601.08221",
"version": "v1"
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