Damping of gravitational waves in matter and Λ−dominated era

The goal of this paper is studying the integro-differential equation of gravitational waves (GWs) in matter-dominated era while the presence of free streaming neutrinos is taken into account via stress tensor with high accuracy. Our focus is on GWs that enter the horizon in the matter dominated era and transmitted to the Λ− dominated era. The results show that the squared amplitude is reduced by  ∼ 3% (61%) in the matter dominated era and this reduction is less after transition for the flat (closed) background. Finally, we compared with the radiation-dominated era for both flat and closed background as well. A stable global topological effect has been inferred from comparison of results for two cases.