Inflating with open strings

We consider the embedding of inflation in Type IIB string theory, with the inflaton given by the position modulus of a D7-brane, an open string. The inflaton potential is sourced by three-form fluxes in the background of the internal space. We study its multi-field dynamics, ignoring first the effects of moduli stabilization, and show that they improve the agreement between observations and predictions. We also study moduli-stabilization in both the Kähler and the complex structure sector. We show that, with a flux tuning, it is possible to have an epoch of inflation in Type IIB string theory with the inflaton an open string modulus.
In addition to embedding inflation in string theory we also consider more generally the structure of Type II string theories compactified in the presence of Dp-branes. We study a string theory realization of the Kalopor-Sorbo mechanism, which provides a field theory argument to constrain the shape of corrections to the scalar potential. For this mechanism it is essential to have couplings between the scalar fields and Minkowski four-forms. We show that in Type II string theories the entire axion scalar potential can be written in terms of these four-forms. We also study α′ corrections to the effective action of Dp-branes. We provide general formulae for the leading order α′ correction to the action of Dp-branes with p = 3,5,7 and provide a supergravity description of the α′ corrections to the D7-brane action, allowing us to study its effects on moduli stabilization.