Constraining exotic high-$z$ reionization histories with Gaussian processes and the Cosmic Microwave Background
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| Format: | Preprint |
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2025
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| _version_ | 1866908606522195968 |
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| author | Cheng, Hanyu Yin, Ziwen Di Valentino, Eleonora Marsh, David J. E. Visinelli, Luca |
| author_facet | Cheng, Hanyu Yin, Ziwen Di Valentino, Eleonora Marsh, David J. E. Visinelli, Luca |
| contents | The large-angle polarization anisotropies in the Cosmic Microwave Background (CMB) arise from Thomson scattering of CMB photons off free electrons in the post-recombination Universe. In the standard $Λ$ cold dark matter cosmological model, the free electron density increases at redshifts $z \lesssim 10$ as the first stars form, reionizing the intergalactic medium. We use \emph{Gaussian processes} to perform a model-independent reconstruction of the cosmic reionization history constrained by \textit{Planck} CMB data. Our approach recovers the standard reionization at $z \lesssim 10$ and places stringent limits on any additional high-$z$ reionization. From this reconstruction, we define a new derived parameter, the high-redshift contribution to the CMB optical depth, $τ_{\mathrm{highz}}$, whose posterior distribution provides robust constraints on exotic energy injection scenarios. We demonstrate this for decaying dark matter with particle masses in the range $\mathcal{O}(1\,\text{MeV})$. A companion paper applies this framework to multi-axion models. All data and code are publicly available at: \href{https://github.com/Cheng-Hanyu/CLASS_reio_gpr}{github.com/Cheng-Hanyu/CLASS\_reio\_gpr}. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_19096 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Constraining exotic high-$z$ reionization histories with Gaussian processes and the Cosmic Microwave Background Cheng, Hanyu Yin, Ziwen Di Valentino, Eleonora Marsh, David J. E. Visinelli, Luca Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology The large-angle polarization anisotropies in the Cosmic Microwave Background (CMB) arise from Thomson scattering of CMB photons off free electrons in the post-recombination Universe. In the standard $Λ$ cold dark matter cosmological model, the free electron density increases at redshifts $z \lesssim 10$ as the first stars form, reionizing the intergalactic medium. We use \emph{Gaussian processes} to perform a model-independent reconstruction of the cosmic reionization history constrained by \textit{Planck} CMB data. Our approach recovers the standard reionization at $z \lesssim 10$ and places stringent limits on any additional high-$z$ reionization. From this reconstruction, we define a new derived parameter, the high-redshift contribution to the CMB optical depth, $τ_{\mathrm{highz}}$, whose posterior distribution provides robust constraints on exotic energy injection scenarios. We demonstrate this for decaying dark matter with particle masses in the range $\mathcal{O}(1\,\text{MeV})$. A companion paper applies this framework to multi-axion models. All data and code are publicly available at: \href{https://github.com/Cheng-Hanyu/CLASS_reio_gpr}{github.com/Cheng-Hanyu/CLASS\_reio\_gpr}. |
| title | Constraining exotic high-$z$ reionization histories with Gaussian processes and the Cosmic Microwave Background |
| topic | Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2506.19096 |