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.