Delta-gravity and Dark Energy
  We present a model of the gravitational field based on two symmetric tensors.
The equations of motion of test particles are derived: Massive particles do not
follow a geodesic but massless particles trajectories are null geodesics of an
effective metric. Outside matter, the predictions of the model coincide exactly
with General Relativity, so all classical tests are satisfied. In Cosmology, we
get accelerated expansion without a cosmological constant.
