Constraining inverse-curvature gravity with supernovae.

We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07<or=omegam<or=0.21 (95% C.L.). Hence the inverse-curvature gravity models considered cannot explain the dynamics of the Universe just with a baryonic matter component.