Ulrich Theis

Nonperturbative corrections to 4D string theory effective actions from SL(2,Z) duality and supersymmetry

We find the D(-1)- and D1-brane instanton contributions to the hypermultiplet moduli space of type IIB string compactifications on Calabi-Yau threefolds. These combine with known perturbative and world sheet instanton corrections into a single modular invariant function that determines the hypermultiplet low-energy effective action.

N = 2 supersymmetric scalar-tensor couplings

We determine the general coupling of a system of scalars and antisymmetric tensors, with at most two derivatives and undeformed gauge transformations, for both rigid and local N = 2 supersymmetry in four-dimensional spacetime. Our results cover interactions of hyper, tensor and double-tensor multiplets and apply among others to Calabi-Yau threefold compactifications of type II supergravities. As an example, we give the complete lagrangian and supersymmetry transformation rules of the double-tensor multiplet dual to the universal hypermultiplet.

Membrane instantons and de Sitter vacua

We investigate membrane instanton effects in type-IIA strings compactified on rigid Calabi-Yau manifolds. These effects contribute to the low-energy effective action of the universal hypermultiplet. In the absence of additional fivebrane instantons, the quaternionic geometry of this hypermultiplet is determined by solutions of the three-dimensional Toda equation. We construct solutions describing membrane instantons, and find perfect agreement with the string theory prediction. In the context of flux compactifications we discuss how membrane instantons contribute to the scalar potential and the stabilization of moduli. Finally, we demonstrate the existence of meta-stable de Sitter vacua.

N = 2 rigid supersymmetry with gauged central charge

Abstract We develop a general setting for N = 2 rigid supersymmetric field theories with gauged central charge in harmonic superspace. We consider those N = 2 multiplets which have a finite number of off-shell components and exist off shell owing to a non-trivial central charge. This class includes, in particular, the hypermultiplet with central charge and various versions of the vector-tensor multiplet. For such theories we present a manifestly supersymmetric universal action. Chern-Simons couplings to an external N = 2 super Yang-Mills multiplet are given, in harmonic superspace, for both the linear and non-linear vector-tensor multiplets with gauged central charge. We show how to deduce the linear version of the vector-tensor multiplet from six dimensions.

Instanton Solutions for the Universal Hypermultiplet

We expand our previous analysis on fivebrane and membrane instanton solutions in the universal hypermultiplet, including near-extremal multi-centered solutions and mixed fivebrane-membrane charged instantons. The results are most conveniently described in terms of a double-tensor multiplet.

On de Sitter vacua in type IIA orientifold compactifications

Abstract This Letter discusses the orientifold projection of the quantum corrections to type IIA strings compactified on rigid Calabi–Yau threefolds. It is shown that N = 2 membrane instanton effects give a holomorphic contribution to the superpotential, while the perturbative corrections enter into the Kahler potential. At the level of the scalar potential the corrections to the Kahler potential give rise to a positive energy contribution similar to adding anti-D3-branes in the KKLT scenario. This provides a natural mechanism to lift an AdS vacuum to a meta-stable dS vacuum.

Fivebrane instanton corrections to the universal hypermultiplet

Abstract We analyze the Neveu–Schwarz fivebrane instanton in type IIA string theory compactifications on rigid Calabi–Yau threefolds, in the low-energy supergravity approximation. It there appears as a finite action solution to the Euclidean equations of motion of a double-tensor multiplet (dual to the universal hypermultiplet) coupled to N = 2 , D = 4 supergravity. We determine the bosonic and fermionic zero modes, and the single-centered instanton measure on the moduli space of collective coordinates. The results are then used to compute, in the semiclassical approximation, correlation functions that nonperturbatively correct the universal hypermultiplet moduli space geometry of the low-energy effective action. We find that only the Ramond–Ramond sector receives corrections, and we discuss the breaking of isometries due to instantons.

Masses and dualities in extended Freedman-Townsend models

Abstract We consider some generalizations of Freedman–Townsend models of self-interacting antisymmetric tensors, involving couplings to further form fields introduced by Henneaux and Knaepen. We show how these fields can provide masses to the tensors by means of the Stuckelberg mechanism and implement the latter in four-dimensional N = 1 superspace. The duality properties of the form fields are studied, and the paradoxical situation of a duality between a free and an interacting theory is encountered.

D = 4, N = 1 supersymmetric Henneaux-Knaepen models

Abstract We construct N = 1 supersymmetric versions of four-dimensional Freedman-Townsend models and generalizations thereof found recently by Henneaux and Knaepen, with couplings between 1-form and 2-form gauge potentials. The models are presented both in a superfield formulation with linearly realized supersymmetry and in WZ gauged component form. In the latter formulation the supersymmetry transformations are non-linear and do not commute with all the gauge transformations. Among others, our construction yields N = 1 counterparts of recently found N = 2 supersymmetric gauge theories involving vector-tensor multiplets with gauged central charge.

New N=2 supersymmetric vector-tensor interaction

Abstract An N =2 supersymmetric self-interaction of the vector-tensor multiplet is presented, in which the vector provides the gauge field for local central charge transformations. The dual description in terms of a vector multiplet and an N =1 superspace formulation is given.