Cointegration in functional autoregressive processes

This paper derives a generalization of the Granger-Johansen Representation Theorem valid for H-valued autoregressive (AR) processes, where H is an infinite dimensional separable Hilbert space, under the assumption that 1 is an eigenvalue of finite type of the AR operator function and that no other non-zero eigenvalue lies within or on the unit circle. A necessary and sucient condition for integration of order d = 1, 2,... is given in terms of the decomposition of the space H into the direct sum of d+1 closed subspaces h, h = ,..,d, each one associated with components of the process integrated of order h. These results mirror the ones recently obtained in the nite dimensional case, with the only di erence that the number of cointegrating relations of order 0 is infinite.