Propagation of gravitational waves in the nonperturbative spinor vacuum
  The propagation of gravitational waves on the background of a nonperturbative vacuum of a spinor field is considered. It is shown that there are several distinctive features in comparison with the propagation of plane gravitational waves through empty space: there exists the fixed phase difference between the $h_{yy,zz}$ and $h_{yz}$ components of the wave; the phase and group velocities of gravitational waves are not equal to the velocity of light; the group velocity is always less than the velocity of light; under some conditions the gravitational waves are either damped or absent; for given frequency, there exist two waves with different wave vectors. We also discuss the possibility of experimental verification of the obtained effects as a tool to investigate nonperurbative quantum field theories. 
Vladimir Dzhunushaliev and Vladimir Folomeev
gr-qc hep-th