Chameleon-Graviton-Condensate Cosmology: Resolving Late-Time Acceleration, the Hubble Tension, and Cosmic Structure Constraints

We present Chameleon-Graviton-Condensate Cosmology (CGCC), an effective field theory framework that addresses late-time cosmic acceleration, the H₀ tension, and cosmic structure constraints without relying on a conventional cosmological constant. The model posits that high-energy gravitational processes during early cosmic epochs (such as supermassive black hole accretion) inject Kaluza-Klein (KK) gravitons into a higher-dimensional bulk. Following adiabatic cooling and cascade decays in the bulk, these modes re-enter the 3+1 spacetime via a density-dependent chameleon mechanism. Within low-density cosmic voids, where environmental screening is lifted (mφ → 0), the re-entering gravitons undergo Bose-Einstein condensation (BEC) into a macroscopic infrared ground state. A quartic self-interaction term stabilizes the condensate, yielding an isotropic equation of state with negative pressure ($w=-1$) that dynamically drives void-dominated expansion. We demonstrate that local void expansion reproduces measurements of H₀ ≈ 73 km/s/Mpc, while spatial integration across void-filament boundaries converges to the global Λ CDM-constrained value of H̄₀ ≈ 67.4 km/s/Mpc. Furthermore, the model satisfies strict local constraints from Solar System tests (Cassini bound) and Big Bang Nucleosynthesis (BBN), and offers distinct, falsifiable signatures in weak-lensing shear profiles testable by upcoming astronomical surveys.