{"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/cosmological-implications-of-ultra-light","title":"Cosmological implications of ultra-light axion-like fields","arxiv_id":"1806.10608","date":"2018-06-27","proceeding":null,"authors":["Vivian Poulin","Tristan L. Smith","Daniel Grin","Tanvi Karwal","Marc Kamionkowski"],"abstract":"Cosmological observations are used to test for imprints of an ultra-light axion-like field (ULA), with a range of potentials $V(\\phi)\\propto[1-\\cos(\\phi/f)]^n$ set by the axion-field value $\\phi$ and decay constant $f$. Scalar field dynamics dictate that the field is initially frozen and then begins to oscillate around its minimum when the Hubble parameter drops below some critical value. For $n\\!=\\!1$, once dynamical, the axion energy density dilutes as matter; for $n\\!=\\!2$ it dilutes as radiation and for $n\\!=\\!3$ it dilutes faster than radiation. Both the homogeneous evolution of the ULA and the dynamics of its linear perturbations are included, using an effective fluid approximation generalized from the usual $n=1$ case. ULA models are parameterized by the redshift $z_c$ when the field becomes dynamical, the fractional energy density $f_{z_c} \\equiv \\Omega_a(z_c)/\\Omega_{\\rm tot}(z_c)$ in the axion field at $z_c$, and the effective sound speed $c_s^2$. Using Planck, BAO and JLA data, constraints on $f_{z_c}$ are obtained. ULAs are degenerate with dark energy for all three potentials if $1+z_c \\lesssim 10$. When $3\\times10^4 \\gtrsim 1+z_c \\gtrsim 10 $, $f_{z_c}$ is constrained to be $ \\lesssim 0.004 $ for $n=1$ and $f_{z_c} \\lesssim 0.02 $ for the other two potentials. The constraints then relax with increasing $z_c$. These results strongly constrain ULAs as a resolution to cosmological tensions, such as discrepant measurements of the Hubble constant, or the EDGES measurement of the global 21 cm signal.","url_abs":"https://arxiv.org/abs/1806.10608v1","url_pdf":"https://arxiv.org/pdf/1806.10608v1.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":"cosmological-implications-of-ultra-light","repo_url":"https://github.com/matthewjstott/CMB_axiverse_statistics","is_official":0,"mentioned_in_paper":0,"mentioned_in_github":1,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}