{"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/linear-matter-density-perturbations-in-the-l","title":"Linear matter density perturbations in the $Λ_{\\rm s}$CDM model: Examining growth dynamics and addressing the $S_8$ tension","arxiv_id":"2502.20384","date":"2025-02-27","proceeding":null,"authors":["Özgür Akarsu","Arman Çam","Evangelos A. Paraskevas","Leandros Perivolaropoulos"],"abstract":"We investigate linear matter density perturbations in the $\\Lambda_{\\rm s}$CDM, in which the $\\Lambda$ is replaced by late-time ($z\\sim2$) mirror AdS-dS transition, resulting in distinct growth dynamics. We use two complementary approaches: (i) determining the initial density contrast and its evolution rate for a given collapse scale factor, (ii) computing the collapse scale factor for a specified initial density contrast and evolution rate. We derive analytical solutions for the growth rate $f=\\Omega_{\\rm m}^\\gamma$ and growth index $\\gamma$ in both models. Prior to the transition, the AdS-like $\\Lambda$ reduces cosmic friction, causing linear matter density perturbations to grow more rapidly than in $\\Lambda$CDM; this effect is most pronounced just before the transition, with a growth rate around $15\\%$ higher than $\\Lambda$CDM around $z\\sim2$. After the transition, $\\Lambda_{\\rm s}$CDM behaves similarly to $\\Lambda$CDM but features a larger cosmological constant, leading to higher $H(z)$ and greater cosmic friction that more effectively suppresses growth. Before the transition, $\\gamma$ remains below both the $\\Lambda$CDM and EdS values ($\\gamma\\approx6/11$); during the transition, it increases rapidly and then grows gradually, paralleling $\\Lambda$CDM while remaining slightly higher in the post-transition era-though overall, it stays near $\\gamma\\sim0.55$. Using the Planck best-fit values, $\\Omega_{\\rm m0}=0.28$ for $\\Lambda_{\\mathrm{s}}$CDM and $\\Omega_{\\rm m0}=0.32$ for $\\Lambda$CDM, we find $f=0.49$ and $f=0.53$, respectively. $\\Lambda_{\\rm s}$CDM predicts a value of $f=0.48$, recently obtained from LSS data when $\\gamma$ is treated as a free parameter in $\\Lambda$CDM. This suggests that $\\Lambda_{\\rm s}$CDM may resolve the structure growth anomaly, without deviating from $\\gamma \\sim 0.55$.","url_abs":"https://arxiv.org/abs/2502.20384v1","url_pdf":"https://arxiv.org/pdf/2502.20384v1.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":"linear-matter-density-perturbations-in-the-l","repo_url":"https://github.com/camarman/MDP-Ls","is_official":1,"mentioned_in_paper":0,"mentioned_in_github":1,"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}