Quantum–kinetic dark energy (QKDE) is tested against current cosmological observations. The model provides a covariantly completed scalar–tensor framework in which the kinetic normalization of a scalar field acquires a controlled time dependence while preserving diffeomorphism invariance. Within the effective field theory description of dark energy, QKDE occupies an αₖ-only sector characterized by αB = αM = αT = αH = 0 corresponding to a constant effective Planck mass, luminal tensor propagation, and the absence of gravitational slip. The background evolution is solved numerically in e-fold time, and the resulting expansion history is mapped to a tabulated equation of state for use in linear perturbation calculations. The model is interfaced with a Boltzmann solver to compute CMB anisotropies and matter clustering observables. Constraints are derived from Type Ia supernovae, baryon acoustic oscillation measurements, compressed CMB distance information, and redshift-space distortion measurements of fσ₈. Model comparison relative to a ΛCDM baseline is performed using χ² statistics together with standard information criteria. No statistically significant preference for QKDE over ΛCDM is found within stable and physically admissible regions of parameter space. Parameter combinations that produce observable deviations in the expansion history or growth rate are tightly constrained by geometric and CMB probes, and viable solutions converge toward the ΛCDM limit. Linear CMB temperature and polarization spectra remain indistinguishable from ΛCDM at current observational precision. These results place quantitative bounds on covariantly completed αₖ-only dark energy sectors and highlight the constraining power of contemporary high-precision cosmological data.
Daniel Brown (Mon,) studied this question.