We discuss a nonlocal modification of gravity obtained adding a term m ^ { 2 } R \Box ^ { -2 } R to the Einstein-Hilbert action .
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 = { \cal O } ( H _ { 0 } ) 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 _ { DE } \simeq - 1.14 .
This value is consistent with the existing data , and could also resolve the possible tension between the Planck data and local measurements of the Hubble parameter .