On α′-effects from D-branes in 4dN=1

In this work we study type IIB Calabi-Yau orientifold compactifications in the presence of space-time filling D7-branes and O7-planes. In particular, we conclude that alpha ' (2)g(s)-corrections to their DBI actions lead to a modification of the four-dimensional N = 1 Kahler potential and coordinates. We focus on the one-modulus case of the geometric background i.e. h(1,1) = 1 where we find that the alpha ' (2)g(s)-correction is of topological nature. It depends on the first Chern form of the four-cycle of the Calabi-Yau orientifold which is wrapped by the D7-branes and O7-plane. This is in agreement with our previous F-theory analysis and provides further evidence for a potential breaking of the no-scale structure at order alpha ' (2)g(s). Corrected background solutions for the dilaton, the warp-factor as well as the internal space metric are derived. Additionally, we briefly discuss alpha ' -corrections from other Dp-branes.