{"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/probing-new-physics-with-high-redshift","title":"Probing New Physics with High-Redshift Quasars: Axions and Non-standard Cosmology","arxiv_id":"2309.07212","date":"2023-09-13","proceeding":null,"authors":["Chen Sun","Manuel A. Buen-Abad","JiJi Fan"],"abstract":"The Hubble diagram of quasars, as candidates to ``standardizable\" candles, has been used to measure the expansion history of the Universe at late times, up to very high redshifts ($z \\sim 7$). It has been shown that this history, as inferred from the quasar dataset, deviates at $\\gtrsim 3 \\sigma$ level from the concordance ($\\Lambda$CDM) cosmology model preferred by the cosmic microwave background (CMB) and other datasets. In this article, we investigate whether new physics beyond $\\Lambda$CDM (B$\\Lambda$CDM) or beyond the Standard Model (BSM) could make the quasar data consistent with the concordance model. We first show that an effective redshift-dependent relation between the quasar UV and X-ray luminosities, complementing previous phenomenological work in the literature, can potentially remedy the discrepancy. Such a redshift dependence can be realized in a BSM model with axion-photon conversion in the intergalactic medium (IGM), although the preferred parameter space is {in tension with various other astrophysical constraints on axions, at a level} depending on the specific assumptions made regarding the IGM magnetic field. We briefly discuss a variation of the axion model that could evade these astrophysical constraints. On the other hand, we show that models beyond $\\Lambda$CDM such as one with a varying dark energy equation of state ($w$CDM) or the phenomenological cosmographic model with a polynomial expansion of the luminosity distance, cannot alleviate the tension. The code for our analysis, based on \\texttt{emcee}~\\cite{Foreman_Mackey_2013} and \\texttt{corner.py}~\\cite{corner}, is publicly available at \\href{https://github.com/ChenSun-Phys/high\\_z\\_candles.git}{{\\tt github.com/ChenSun-Phys/high\\_z\\_candles}}.","url_abs":"https://arxiv.org/abs/2309.07212v2","url_pdf":"https://arxiv.org/pdf/2309.07212v2.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":"probing-new-physics-with-high-redshift","repo_url":"https://github.com/chensun-phys/high_z_candles","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}