Completing Einstein Gravity with a Single Scalar: Cosmic History without Dark Matter or Dark Energy

We present a scalar–tensor completion of Einstein gravity, based on the MMA-DMF [1] in which a single light scalar field ϕ replaces both cold dark matter and dark energy at the level of cosmological phenomenology. The model is formulated as an effective field theory (EFT) valid below a cutoff scale Λ, with screened fifth forces on small scales [2] and a controlled modification of the background expansion and the growth of structure at late times. We show how a non-singular “reset” phase, an early-time bump in the expansion rate, a standard radiation and baryon dominated era, the present acceleration and a future turnaround can all be obtained from one scalar potential and its coupling to matter, without introducing additional dark fluids. We summarise the agreement with CMB [3], BAO, H0 and large-scale structure observables obtained in previous phenomenological studies of this model.