Asymptotic Conformal Invariance via Dynamically Coupled Scalar-Tensor Quintessence with Environmental Chameleon Screening

We present a self-consistent, non-perturbative Scalar-Tensor framework where a rolling cosmic quintessence field ϕ is non-minimally coupled to both the gravitational Ricci scalar R and the fermion sector ψ. This framework maps a fields-and-spikes ontology, wherein classical matter emerges as localized energy packets within fundamental continuous fields. The model provides a unified mechanism for late-time cosmic acceleration—matching recent Dark Energy Spectroscopic Instrument (DESI) dynamical observations—while taming the ultraviolet (UV) divergences of quantum gravity via an asymptotically decaying gravitational coupling G(ϕ). To satisfy local highprecision constraints from the MICROSCOPE satellite experiment, the framework natively embeds a density-dependent Chameleon screening mechanism. By enforcing an Einstein-frame constraint β <√︁2/3/Mpl and utilizing an exponential tracking potential, we mathematically eliminate Ostrogradsky ghost instabilities and the cosmological constant fine-tuning problem. Finally, we calculate the exact vanishing of the quantum trace anomaly (⟨Tμμ ⟩ = 0) at the future limit, proving that the universe achieves absolute scale invariance, providing a smooth geometric transition through the conformal boundary.