THERMAL SCIENCE, cilt.26, 2022 (SCI-Expanded)
The semilinear Klein-Gordon equation with initial conditions is studied in de Sitter spacetime. The L-infinity decay estimates are derived for the solutions to the linear Klein- Gordon equations with and without source term in de Sitter spacetime. It is also showed the global existence of solutions to the initial value problem with power type non-linear terms for small initial data by using these estimates.