URSF-R1: A Phenomenological Late-Time Growth-Suppression Kernel for Low-Redshift Structure Tension

This standalone release presents URSF-R1, a phenomenological late-time, scale-dependent growth-suppression kernel implemented in CLASS. URSF-R1 modifies the linear matter power spectrum while leaving the LCDM background expansion unchanged. The purpose of the study is to test whether controlled suppression of late-time growth can improve low-redshift growth diagnostics without altering BAO/background geometry. This release should be interpreted as a reproducible diagnostic manuscript and supporting package. It is not a claim of confirmed new physics, nor a complete cosmological model. AI Assistance Disclosure This work was prepared by Malin Hess with assistance from AI tools, including OpenAI’s ChatGPT. AI assistance was used for research support, mathematical checking, code/debugging guidance, result organization, manuscript drafting, editing, formatting, and report preparation. All conceptual claims, interpretive choices, final wording, numerical results, and responsibility for the contents of this work remain with the author. AI-generated suggestions were reviewed, edited, and accepted or rejected by the author. This disclosure is provided for transparency.