Dark energy as a massive vector field

We propose that the Universe is filled with a massive vector field non-minimally coupled to gravitation. The field equations of the model are consistently derived, and their application to cosmology is considered. The Friedmann equations acquire an extra dark-energy component, which is proportional to the mass of the vector particle. This leads to a late-time accelerated de Sitter type expansion. The free parameters of the model (gravitational coupling constants and initial value of the cosmological vector field) can be estimated by using the PPN solar system constraints. The mass of the cosmological massive vector particle, which may represent the main component of the Universe, is of the order of 10^-63 g. PACS 03.70.+k; 11.90.+t; 11.10.Kk