Spin 2 Field Equation in Expanding Universe

The spin 2 field equations are separated in the Robertson-Walker space-time by the Newman-Penrose formalism and by using a null tetrad frame previously considered. The angular and radial separated equations are integrated by generalizing and improving results relative to the massless case. The separated time equations are governed by two coupled linear differential equations that depend on the cosmological background. They are solved and studied for some models of cosmological expansion such as the linear and exponential expansion and the matter dominated and radiative expansion of the standard cosmology.