Axion-Photon Conversion in FLRW with Primordial Magnetic Fields: Explaining the Radio Excess
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| Format: | Preprint |
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2025
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| _version_ | 1866912583235141632 |
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| author | Setabuddin Haque, Md Riajul Karmakar, Rajesh Pal, Supratik |
| author_facet | Setabuddin Haque, Md Riajul Karmakar, Rajesh Pal, Supratik |
| contents | We explore the possibility of axion-photon conversion as a common origin of two low-frequency anomalies: the isotropic radio excess (ARCADE2) and the deep global 21-cm absorption trough (EDGES). From the axion-photon action in an FLRW background with primordial magnetic fields (PMFs), we derive the scale-dependent conversion probability including plasma effects. Resonant conversion, arising when the axion mass matches the plasma-induced photon mass, produces soft photons in the MHz-GHz range. By modeling stochastic PMFs with amplitude $B_0$ and spectral index $n_{\rm B}$, we show that axion-like particles with mass $\sim 10^{-14}$-$10^{-12}\,\mathrm{eV}$ and nanogauss-level nearly scale invariant PMFs can explain both ARCADE2 and EDGES. Heating from PMF dissipation via ambipolar diffusion and turbulent decay reduces the 21-cm trough, shifting the viable parameter space. Our results stem from a consistent theoretical framework developed from first principles and a combined analysis of the radio excess and global 21-cm signal, while remaining consistent with CMB bounds on PMFs and $ΔN_{\rm eff}$. We conclude that global 21-cm observations may offer potential sensitivity to axions, primordial magnetism, and dark-sector physics. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_09472 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Axion-Photon Conversion in FLRW with Primordial Magnetic Fields: Explaining the Radio Excess Setabuddin Haque, Md Riajul Karmakar, Rajesh Pal, Supratik Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology We explore the possibility of axion-photon conversion as a common origin of two low-frequency anomalies: the isotropic radio excess (ARCADE2) and the deep global 21-cm absorption trough (EDGES). From the axion-photon action in an FLRW background with primordial magnetic fields (PMFs), we derive the scale-dependent conversion probability including plasma effects. Resonant conversion, arising when the axion mass matches the plasma-induced photon mass, produces soft photons in the MHz-GHz range. By modeling stochastic PMFs with amplitude $B_0$ and spectral index $n_{\rm B}$, we show that axion-like particles with mass $\sim 10^{-14}$-$10^{-12}\,\mathrm{eV}$ and nanogauss-level nearly scale invariant PMFs can explain both ARCADE2 and EDGES. Heating from PMF dissipation via ambipolar diffusion and turbulent decay reduces the 21-cm trough, shifting the viable parameter space. Our results stem from a consistent theoretical framework developed from first principles and a combined analysis of the radio excess and global 21-cm signal, while remaining consistent with CMB bounds on PMFs and $ΔN_{\rm eff}$. We conclude that global 21-cm observations may offer potential sensitivity to axions, primordial magnetism, and dark-sector physics. |
| title | Axion-Photon Conversion in FLRW with Primordial Magnetic Fields: Explaining the Radio Excess |
| topic | Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2509.09472 |