Vector models for dark energy
  We explore the possibility that the present stage of accelerated expansion of the universe is due to the presence of a cosmic vector field. We show that vector theories allow for the generation of an accelerated phase without the introduction of potential terms or unnatural scales in the Lagrangian. We propose a particular model with the same number of parameters as LCDM and excellent fits to SNIa data. The model is scaling during radiation era, with natural initial conditions, thus avoiding the cosmic coincidence problem. Upcoming observations will be able to clearly discriminate it from standard LCDM cosmology 
Jose Beltran Jimenez, Antonio L. Maroto