We propose a scenario for realizing super-Planckian axion decay constants in Calabi-Yau orientifolds of type IIB string theory, leading to large-field inflation. Our construction is a simple embedding in string theory of the mechanism of Kim, Nilles, and Peloso, in which a large effective decay constant arises from alignment of two smaller decay constants. The key ingredient is gaugino condensation on magnetized or multiply-wound D7-branes. We argue that, under very mild assumptions about the topology of the Calabi-Yau, there are controllable points in moduli space with large effective decay constants.

We analyze properties of non-supersymmetric isometry-preserving perturbations to the infrared region of the warped deformed conifold, i.e. the KlebanovStrassler solution. We discuss both perturbations that "squash" the geometry, so that the internal space is no longer conformally Calabi-Yau, and perturbations that do not squash the geometry. Among the perturbations that we discuss is the solution that describes the linearized near-tip backreaction of a smeared collection of D3-branes positioned in the deep infrared. Such a configuration is a candidate gravity dual of a non-supersymmetric state in a large-rank cascading gauge theory. Although D3-branes do not directly couple to the 3-form flux, we argue that, due to the presence of the background imaginary self-dual flux, D3-branes in the Klebanov-Strassler geometry necessarily produce singular non-imaginary self-dual flux. Moreover, since conformally Calabi-Yau geometries cannot be supported by non-imaginary self-dual flux, the D3-branes squash the geometry as our explicit solution shows. We also briefly discuss supersymmetry-breaking perturbations at large radii and the effect of the nonsupersymmetric perturbations on the gravitino mass.

We revisit the analysis of effective field theories resulting from non-supersymmetric perturbations to supersymmetric flux compactifications of the type-IIB superstring with an eye towards those resulting from the backreaction of a small number of anti-D3-branes. Independently of the background, we show that the low-energy Lagrangian describing the fluctuations of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite perturbations to marginal operators that were not fully considered in some previous treatments. We take this as an indication that the breaking of supersymmetry by anti-D3-branes or other sources may be spontaneous rather than explicit. In support of this, we consider the action of an anti-D3-brane probing an otherwise supersymmetric configuration and identify a candidate for the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte

We analyze the wavefunctions for open strings in warped compactifications, and compute the warped Kähler potential for the light modes of a probe D-brane. This analysis not only applies to the dynamics of D-branes in warped backgrounds, but also allows to deduce warping corrections to the closed string Kähler metrics via their couplings to open strings. We consider in particular the spectrum of D7-branes in warped Calabi-Yau orientifolds, which provide a string theory realizations of the Randall-Sundrum scenario. We find that certain background fluxes, necessary in the presence of warping, couple to the fermionic wavefunctions and qualitatively change their behavior. This modified dependence of the wavefunctions are needed for consistency with supersymmetry, though it is present in non-supersymmetric vacua as well. We discuss the deviations of our setup from the RS scenario and, as an application of our results, compute the warping corrections to Yukawa couplings in a simple model. Our analysis is performed both with and without the presence of D-brane world-volume flux, as well as for the case of backgrounds with varying dilaton. 4 Roughly speaking, (2.5) is invariant under the transformation Θ → Θ + P D7 − κ, with κ an arbitrary 10D MW bispinor. One can then use this symmetry to remove half of the degrees of freedom in Θ.5 In our conventions the chirality matrix for a D(2k + 2)-brane in R 1,2k+1 is Γ (2k+2) = i k Γ 0...2k+1 , where Γ i are flat Γ-matrices. For instance, a D7-brane extended along the directions 0 . . . 7 has Γ (8) = −iΓ 01234567 .