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Denis Klevers

I am interested in aspects of effective four-dimensional theories arising from string compactifications and their connecting dualities. In this context, the examination of geometrical properties of the compactification geometry is often crucial for the understanding of the physics of the four-dimensional effective theories. My early research covered the study of heterotic orbifold compactifications and their smooth blow-up Calabi-Yau threefolds. Then I moved on to the study of D-branes in Type II and F-theory compactifications. In these theories the exact calculation of holomorphic coupling functions, most notably the superpotential, in the N=1 supersymmetric effective theory is possible. For this calculation I explicitly determined the D5-brane effective action, which relates the effective superpotential to geometric quantities, the periods and certain chain-integrals on the Calabi-Yau threefold. In subsequent works, methods from string dualities like mirror symmetry for Calabi-Yau threefolds and open strings as well as for Calabi-Yau fourfolds relevant for F-theory compactifications were used to calculate these geometrical objects explicitly. Further connections to heterotic compactifications could be drawn exploiting heterotic/F-theory duality for heterotic five-branes. Finally a novel type of duality was proposed relating a compactification with D5- or M5-branes to a dual flux compactification with SU(3)-structure. My current work is focused on an application and extension of the geometrical and String-duality related methods to improve the understanding of non-perturbative string effects in compactifications with N=1 supersymmetry.