Dynamics of the quantum vacuum: Cosmology as relaxation to the   equilibrium state
  The behavior of the gravitating vacuum energy density in an expanding universe is discussed. A scenario is presented with a step-wise relaxation of the vacuum energy density. The vacuum energy density moves from plateau to plateau and follows, on average, the steadily decreasing matter energy density. The current plateau with a small positive value of the vacuum energy density (effective cosmological constant) may result from a still not equilibrated contribution of the light massive neutrinos to the quantum vacuum. 
F.R. Klinkhamer, G.E.Volovik
gr-qc astro-ph.CO hep-ph