Relaxation-Driven Cyclic Cosmology (RDCC) v25.0 - Minimal Extension of ΛCDM / Bounce EFT Framework

This work presents Relaxation-Driven Cyclic Cosmology (RDCC) v25.0, formulated as a minimal extension of the ΛCDM cosmological framework within an effective field theory (EFT) bounce scenario. The model explores a cyclic cosmological evolution driven by a relaxation mechanism associated with a scalar field sector that dynamically links several cosmological observables. The central idea of RDCC is that a single relaxation parameter (α) governs multiple cosmological sectors simultaneously. Within this framework, the parameter couples the dynamics of cyclic background evolution to several observable quantities, including potential contributions to ΔNeff, the dark matter–baryon ratio, and deviations in large-scale structure growth. The model is formulated using standard EFT methods for cosmological perturbations and includes a cuscuton-like modification enabling a non-singular bounce while maintaining perturbative stability conditions. Version v25.0 introduces several refinements compared to previous iterations of the RDCC framework, including: an explicit perturbative stability analysis at quadratic order, a derivation of the effective sound speed from the scalar-field Lagrangian, clarification of bounce matching conditions within a CPT-symmetric cyclic scenario, improved discussion of observational signatures potentially testable by future experiments. The work is presented as an exploratory theoretical framework rather than a complete cosmological model. Its goal is to investigate whether a minimal EFT-based cyclic extension of the ΛCDM paradigm can consistently relate several cosmological observables through a common dynamical parameter. RDCC v25.0 represents an iterative stage in the development of the framework, and future versions may expand the perturbative treatment, numerical evolution across the bounce, and detailed observational constraints. This version supersedes RDCC v24.0 and continues the ongoing development of the Relaxation-Driven Cyclic Cosmology framework. This version builds on: Relaxation-Driven Cyclic Cosmology (RDCC) v1.0: A Minimal Eternal Framework and Its Dynamical Realization: https://zenodo.org/records/18281686 Relaxation-Driven Cyclic Cosmology (RDCC) v2.0: A Minimal Eternal Framework with Dynamical Realization and Extensions: https://zenodo.org/records/18304744 Relaxation-Driven Cyclic Cosmology (RDCC) v5.0: Bounce-Matching Formalism, Mirror-Sector Dynamics, and Refined Gravitational Waves: https://zenodo.org/records/18307836 Relaxation-Driven Cyclic Cosmology (RDCC) v6.0: Black Hole Bounces as Local CPT-Fixpoints, Full Perturbation Transfer Matrix and Mirror-Sector Microphysics: https://zenodo.org/records/18312656 Relaxation-Driven Cyclic Cosmology (RDCC) v7.0: Quantum-Corrected Black Hole Bounces, Full Perturbation Transfer Matrix with Phase-Shift, and Mirror Microphysics https://zenodo.org/records/18327084 Relaxation-Driven Cyclic Cosmology (RDCC) v8.0: Parameter Space Exploration, Data Confrontation, and Predictive Structure Formation https://zenodo.org/records/18334398 Relaxation-Driven Cyclic Cosmology (RDCC) v9.0: Predictive Cosmology, Nonlinear Structure Formation, and Astrophysical Signatures https://zenodo.org/records/18336237 Relaxation-Driven Cyclic Cosmology (RDCC) v10.0: Unified Cosmology, Full Simulations, and Observational Pipelines https://zenodo.org/records/18336865 Relaxation-Driven Cyclic Cosmology (RDCC) v11.0: Entropy Dynamics, Mirror Thermodynamics, EFT Consistency, and Naturalness https://zenodo.org/records/18341147 Relaxation-Driven Cyclic Cosmology (RDCC) v12.0: Precision Predictions, Multi-Probe Confrontation, and Quantum-Geometric Completion https://zenodo.org/records/18346555 Relaxation-Driven Cyclic Cosmology (RDCC) v13.0: Quantum Completion, Global Consistency, and Predictive Cosmology https://zenodo.org/records/18348450 Relaxation-Driven Cyclic Cosmology (RDCC) v14.0: Unified Quantum Gravity, Full-Cycle Simulation, and Multi-Messenger Precision Cosmology https://zenodo.org/records/18351916 Relaxation-Driven Cyclic Cosmology (RDCC) v15.0: Mirror-Sector Cosmology, Hidden-Universe Gravitational Waves, and Two-Sector Evolution https://zenodo.org/records/18358095 Relaxation-Driven Cyclic Cosmology (RDCC) v16.0: Precision Two-Sector Dynamics, Mirror Thermodynamics Refinements, and Enhanced GW Forecasts https://zenodo.org/records/18388123 Relaxation-Driven Cyclic Cosmology (RDCC) v17.0 - Minimal Effective Two-Sector Version https://zenodo.org/records/18761806 While the core of RDCC remains a structural, timeless framework with fixpoint character, this document explores a dynamical realization of the bounce mechanism to enable concrete, falsifiable predictions. Related documents and the full RDCC ecosystem are available via Zenodo:https://zenodo.org/records/18204087 Michael Lehmannmi.lehmann@gmx.de