2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/197522We derive boundary states which describe configurations of multiple parallel branes with arbitrary open string states interactions in bosonic string theory. This is obtained by a careful discussion of the factorization of open/closed string states amplitudes taking care of cycles needed by ensuring vertexes commutativity: in particular the discussion reveals that already at the tree level open string knows of the existence of closed string. We also give a formal expression for computing pure closed string amplitudes using the open string formalism.39 pages. Improved explanations and corrected some misprints. Version to be published in NPBHigh Energy Physics - Theorytext