φ-conformal cosmology: a unified scalar field model for inflation, dark energy, and the mirror sector

We present a cosmological model based on a conformally coupled scalar field φ with a quartic potential V (φ) =λφ⁴/4 and non-minimal coupling ξφ²R to gravity. The two free parameters are λ=0. 30, fixed by the observed dark energy equation of state w₀=−0. 727 (DESI 2024), and ξ=0. 00226, fixed by the scalar spectral index nₛ=0. 9649 (Planck 2018). The model makes four independent falsifiable predictions: (i) a tensor-to-scalar ratio r≈0. 0014, within reach of LiteBIRD (2028) ; (ii) suppression of CMB power at low multipoles with characteristic scale ℓ_φ≈2. 82, consistent with the observed quadrupole deficit; (iii) a C× (φ→−φ) symmetry that places antimatter in a causally disconnected mirror sector, naturally explaining the baryon asymmetry and providing a dark matter candidate; (iv) a gravitational wave background enhancement factor of ≈1. 22 from mirror-sector sources, consistent with the NANOGrav 2023 excess at 0. 5σ. No parameters are adjusted to fit these four observables simultaneously.