dS Spaces and Brane Worlds in Exotic String Theories.

We investigate string-phenomenological questions of Hull's exotic superstring theories with Euclidean strings/branes and multiple times. These are known to be plagued by pathologies like the occurrence of ghosts. On the other hand, these theories exhibit de Sitter solutions. Our special focus lies on the question of the coexistence of such de Sitter solutions and ghost-free brane worlds. To this end, the world-sheet CFT description of Euclidean fundamental strings is generalized to include also the open string/D-brane sector. Demanding that in the "observable" gauge theory sector the gauge fields themselves are non-ghosts, a generalization of the dS swampland conjecture is found.