Gaugino condensation and nonperturbative superpotentials in flux compactifications -: art. no. 074

There are two known sources of nonperturbative superpotentials for Kahler moduli in type IIB orientifolds, or F-theroy compactifications on Calabi-Yau fourfolds, with flux: euclidean brane instantons and low-energy dynamics in D7 brane gauge theories. The first class of effects, euclidean D3 branes which lift in M-theory to M5 branes wrapping divisors of arithmetic genus 1 in the fourfold, is relatively well understood. The second class has been less explored. In this paper, we consider the explicit example of F-theroy on K3 x K3 with flux. The fluxes lift the D7 brane matter fields, and stabilize stacks of D7 branes at loci of enhanced gauge symmetry. The resulting theories exhibit gaugino condensation, and generate a nonperturbative superpotential for Kahler moduli. We describe how the relevant geometries in general contain cycles of arithmetic genus X greater than or equal to 1 (and how X > 1 divisors can contribute to the superpotential, in the presence of flux). This second class of effects is likely to be important in finding even larger classes of models where the KKLT mechanism of moduli stabilization can be realized. We also address various claims about the situation for IIB models with a single Kahler modulus.