Generation of gravitational waves by generic sources in de Sitter space-time

We study the generation of gravitational radiation by sources moving in the de Sitter background. Exploiting the maximal symmetry and the conformal flatness of de Sitter space-time we prove that the derivation of this gravitational radiation can be done along the same lines as in Minkowski space-time. A gauge is chosen in which all the physical and unphysical modes of the graviton are those of a minimally coupled massless scalar field in de Sitter space-time and a massless field in Minkowski space-time. The graviton retarded Green's function and the Schwinger commutator function are computed in this gauge using Quantum Field Theory techniques. We obtain closed formulae for the spectral decomposition in frequencies of the linaearized gravitational field produced by the source, in terms of a suitable spectral decomposition of the source energy-momentum tensor. This spectral decomposition is dictated by the free (sourceless) gravitational wave modes in the de Sitter background