This paper is focused on the study of modal logics defined from valued Kripke frames, and particularly, on computability and expressivity questions of modal logics of transitive Kripke frames evaluated over certain residuated lattices. It is shown that a large family of those logics -including the ones arising from the standard MV and Product algebras- yields an undecidable consequence relation. Later on, the behavior of transitive modal Lukasiewicz logic is compared with that of its non-transitive counterpart, exhibiting some particulars concerning computability and equivalence with other logics. We conclude the article by showing the undecidability of the validity and the local SAT questions over transitive models when the Delta operation is added to the logic. (C) 2020 Elsevier B.V. All rights reserved.
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