Tensor Modes Damping in Matter and Vacuum Dominated Era
  The present paper has developed an integro-differential equation to propagate
cosmological gravitation waves in matter-dominated era in accounting for the
presence of free streaming neutrinos as a traceless transverse tensor part of
the anisotropic stress tensor. Its focus is on short and long wavelengths of
GWs that enter the horizon in matter-dominated era. Results show that the
anisotropic stress reduces the squared amplitude by $ 0.03\%$ for wavelengths,
entering the horizon during matter-dominated phase. This reduction is less for
those wavelengths that enter the horizon at $ \Lambda $ dominated era in flat
spacetime. All of the calculations have been done in closed spacetime and the
results have been compared with the radiation-dominated case for both flat and
closed spacetimes. Finally the paper investigates the effect of closed
background on the amplitude of the gravitational waves.
