2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/221516We define tensor product decompositions of $E_0$-semigroups with a structure analogous to a classical theorem of Beurling. Such decompositions can be characterized by adaptedness and exactness of unitary cocycles. For CCR-flows we show that such cocycles are convergent.minor corrections, 10 pagesOperator AlgebrasFunctional Analysis46L55; 47D03; 81S25text