Variable separation and solutions of massive field equations of arbitrary spin in Robertson-Walker space-time

The arbitrary spin field equations are separated in the Robertson-Walker space-time by the Newmam-Penrose formalism and by using a null tetrad frame previously considered. The eigenvalue problem of the corresponding separated angular equations is solved by looking for polynomial solutions. The radial separated equations are solved in the flat space-time case and the asymptotic behaviour of the solutions explicited. The separated time equations are studied in elementary situations and in the linear and exponential expansion of the universe. The dependence of the time solutions on increasing spin is pointed out.