Scalar-Cost Dark Energy (SCDE): A Curved-Spacetime QFT–Motivated Kinetic Modification for Late-Time Cosmic Acceleration

The ΛCDM model remains the standard cosmological framework, yet the physical origin of cosmic acceleration is unknown. This work introduces Scalar-Cost Dark Energy (SCDE): a dark-energy model in which the kinetic term of a minimally coupled scalar field acquires a small, redshift-dependent modification. Unlike purely phenomenological constructions, the SCDE kinetic prefactor is motivated by general results in quantum field theory in curved spacetime (QFTCS), where renormalization in an evolving background generically introduces curvature-dependent corrections to the effective action, including mild running of the kinetic normalization. SCDE adopts a minimal two-parameter prefactor K(z)K(z) designed to be negligible at high redshift but to activate smoothly at late times. This activation produces modest, nearly scale-independent modifications to linear structure growth while preserving the ΛCDM background expansion. SCDE does not modify gravity, alter the gravitational-wave speed, or introduce interactions in the dark sector. Instead, it provides a simple, controlled extension of canonical scalar-field dark energy grounded in established QFTCS principles. The model is stable, analytically tractable, easy to implement in cosmological Boltzmann codes, and testable with DESI, Euclid, and LSST.