Gravitational vacuum polarization as an alternative to dark matter
  It is assumed that the quantum vacuum may be studied as consisting of two contributions, with positive and negative energy respectively, which interact but slightly and may be displaced from each other. Then it is proposed that dark matter may be just an increase of the quantum vacuum energy, with respect to the normal dark energy level, induced by the gravitational field of galaxies or clusters. A simple model is worked out able to reproduce astronomical observations. 
E. S. Corchero