• Dark Energy
• Modified Gravity

We discuss a non-local modification of gravity obtained adding a non-local term to the Einstein-Hilbert action, depending on a free mass parameter, m, and on the inverse d'Alembertian applied to the Ricci scalar. We find that the mass parameter m only affects the non-radiative sector of the theory, while the graviton remains massless, there is no propagating ghost-like degree of freedom, no vDVZ discontinuity, and no Vainshtein radius below which the theory becomes strongly coupled.
For m of the order of the present value of the Hubble constant, the theory therefore recovers all successes of GR at solar system and lab scales, and only deviates from it at cosmological scales. We examine the cosmological consequences of the model and we find that it automatically generates a dynamical dark energy and a self-accelerating evolution. After fixing our only free parameter m so to reproduce the observed value of the dark energy density today, we get a pure prediction for the dark energy equation of state,
w~-1.14. This value is in excellent agreement with the Planck result and would also resolve the existing tension between the Planck data and local measurements of the Hubble parameter.