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| Natura: | Preprint |
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2026
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| Accesso online: | https://arxiv.org/abs/2605.24341 |
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| _version_ | 1866914594591604736 |
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| author | Zhang, Kedi Yin, Lu |
| author_facet | Zhang, Kedi Yin, Lu |
| contents | Cosmic birefringence and the Hubble tension represent compelling challenges to the standard $Λ$CDM model. The early dark energy (EDE) model with potentials $V(ϕ) \propto [1-\cos(ϕ/f)]^n$ offer a unified framework to address both anomalies through energy injection near matter-radiation equality and parity-violating Chern--Simons coupling to photons. While previous studies have focused on $n=3$, the dependence of the birefringence signal on the potential index $n$ remains largely unexplored. We perform a comprehensive statistical analysis of axion-like EDE models with $n=2$, $n=3$, and $n=\infty$, using $EB$ cross-polarization data from Planck-$EB$ and ACT-$EB$. The $n=2$ model is severely disadvantaged, displaying extreme coupling values ($gM_{\rm pl} \approx 69.912$ for Planck, $-40.726$ for ACT), large $χ^2_{\rm min}$ (144.52 and 86.93), and $Δχ^2<1$ with many local minials. Conversely, $n=3$ achieves the best fits ($χ^2_{\rm min} = 65.70$ and $48.08$) with consistent couplings ($gM_{\rm pl} = -0.210 \pm 0.024$ and $-0.158 \pm 0.025$) that accurately reproduce observations across all angular scales. We checked that the $n=3$ configuration represents the optimal choice for simultaneously addressing the Hubble tension and cosmic birefringence within a theoretically viable framework. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_24341 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Constraining the Potential Index $n$ of the Early Dark Energy Model Using Cosmic Birefringence from Planck and ACT Zhang, Kedi Yin, Lu Cosmology and Nongalactic Astrophysics Cosmic birefringence and the Hubble tension represent compelling challenges to the standard $Λ$CDM model. The early dark energy (EDE) model with potentials $V(ϕ) \propto [1-\cos(ϕ/f)]^n$ offer a unified framework to address both anomalies through energy injection near matter-radiation equality and parity-violating Chern--Simons coupling to photons. While previous studies have focused on $n=3$, the dependence of the birefringence signal on the potential index $n$ remains largely unexplored. We perform a comprehensive statistical analysis of axion-like EDE models with $n=2$, $n=3$, and $n=\infty$, using $EB$ cross-polarization data from Planck-$EB$ and ACT-$EB$. The $n=2$ model is severely disadvantaged, displaying extreme coupling values ($gM_{\rm pl} \approx 69.912$ for Planck, $-40.726$ for ACT), large $χ^2_{\rm min}$ (144.52 and 86.93), and $Δχ^2<1$ with many local minials. Conversely, $n=3$ achieves the best fits ($χ^2_{\rm min} = 65.70$ and $48.08$) with consistent couplings ($gM_{\rm pl} = -0.210 \pm 0.024$ and $-0.158 \pm 0.025$) that accurately reproduce observations across all angular scales. We checked that the $n=3$ configuration represents the optimal choice for simultaneously addressing the Hubble tension and cosmic birefringence within a theoretically viable framework. |
| title | Constraining the Potential Index $n$ of the Early Dark Energy Model Using Cosmic Birefringence from Planck and ACT |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2605.24341 |