Spinor field equation of arbitrary spin in Robertson-Walker space-time: solution

The study of the field equation of arbitrary spin in Robertson-Walker space time, previously separated by variable separation, is completed. The integration of the separated radial equations is performed in an unified way with respect to the curvature parameter. Through a sequence of transformations on the variable and of the radial function, the radial equation is reported to the Heun’s differential equation. The solution of the Heun’s equation however does fall into the class of known functions such as the hypergeometric, the polynomial, the polynomial-like function, only exceptionally. Moreover the Heun’s differential operator admits of a factorization, a property that would simplify the integration, only for special values of the parameters.