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
hyy,zz and hyz 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.Comment: some change