2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/75194We consider Arveson's problem on the maximality of subdiagonal algebras. We prove that a subdiagonal algebra is maximal if it is invariant under the modular group of a faithful normal state which is preserved by the conditional expectation associated with the subdiagonal algebra.To appear in J. Operator TheoryOperator AlgebrasFunctional Analysis46L10, 47D25text