2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/184511We obtain the one-loop propagators in superstring theory for the general case when the worldsheet fields satisfy non-trivial holonomy and/or boundary conditions. Non-trivial holonomy arises in orbifold and orientifold backgrounds whereas non-trivial boundary conditions arise in backgrounds containing D-branes of different dimensionality or D-branes intersecting each other at an angle. In our derivation, we use a generalized version of the method of images. Dihedral groups play a crucial role in constructing the one-loop propagators.27 pages, significantly extended section 3, minor changes to other sections, references addedHigh Energy Physics - Theorytext