{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/constraining-exotic-high-z-reionization","title":"Constraining exotic high-$z$ reionization histories with Gaussian processes and the cosmic microwave background","arxiv_id":"2506.19096","date":"2025-06-23","proceeding":null,"authors":["Hanyu Cheng","Ziwen Yin","Eleonora Di Valentino","David J. E. Marsh","Luca Visinelli"],"abstract":"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 $\\Lambda$ 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, $\\tau_{\\mathrm{highz}}$, 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}.","url_abs":"https://arxiv.org/abs/2506.19096v1","url_pdf":"https://arxiv.org/pdf/2506.19096v1.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"constraining-exotic-high-z-reionization","repo_url":"https://github.com/cheng-hanyu/class_reio_gpr","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}