Relaxation-Driven Cyclic Cosmology (RDCC) v8.0: Parameter Space Exploration, Data Confrontation, and Predictive Structure Formation This quantitative deepening of RDCC (v8.0) focuses on data confrontation and predictive power. The nonsingular, eternally cyclic model uses a single effective complex scalar field Φ in a tilted double-well potential (tilt from radiative Coleman–Weinberg corrections), driving dynamic dark energy (w_DE > -1) and eternal cycles. A CPT-conjugate mirror sector provides cold dark matter and resolves baryon asymmetry (η_B ≈ 6.1×10^{-10}, Ω_DM/Ω_b ≈ 5.38), preserving global CPT symmetry. Key features in v8.0:- Full parameter space analysis (λ, v, ε, ξ) with allowed regions from Planck, DESI DR2, Euclid, and LISA.- Direct RDCC vs. ΛCDM confrontation: Hubble tension fit (H_0 ≈ 70–73 km/s/Mpc), S_8 ≈ 0.78 (growth modulation), BAO scales (r_s ≈ 147 Mpc), ISW excess ~12.4% (CMB-S4 forecast).- Detailed 21-cm predictions: shifted global dip (~50 mK) and power-spectrum flattening on large scales (SKA/HERA Mid-Array 2028+).- Predictive structure formation: modulated growth factor D(z) and halo mass function shift (Euclid LSS). The model avoids singularities, entropy divergence, flatness issues, inflation, and modified gravity. It positions RDCC as a minimal, data-confronted alternative to ΛCDM. Falsifiability: No GW echoes (LISA/LIGO), S_8 mismatch (Euclid), no BAO modulation (Euclid), ΔN_eff > 0.1 (CMB-S4/BBN), no 21-cm flattening (SKA/HERA). Builds on v7.0 (Zenodo 10.5281/zenodo.18327084) and the full RDCC ecosystem. Full LaTeX source and code snippets in Appendix. 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 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