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Ulrich Theis

Publications and source records attributed to Ulrich Theis.

At least 19 recordsLinked to original sources
arXiv2014

Quantum Corrections in String Compactifications on SU(3) Structure Geometries

We investigate quantum corrections to the classical four-dimensional low-energy effective action of type II string theory compactified on SU(3) structure geometries. Various methods previously developed for Calabi-Yau compactifications are adopted to determine - under some simple assumptions about the low-energy degrees of freedom - the leading perturbative corrections to the moduli space metrics in both alpha' and the string coupling constant. We find - in complete analogy to the Calabi-Yau case - that the corrections take a universal form dependent only on the Euler characteristic of the six-dimensional compact space.

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arXiv2014

Membrane Instantons from Toda Field Theory

Four-dimensional quaternion-Kaehler metrics with an isometry are determined by solutions to the SU($\infty$) Toda equation. We set up a perturbation theory to construct approximate solutions to the latter which can be interpreted as membrane instanton corrections to the moduli space metric of the universal hypermultiplet. We compute one such solution exactly up to the five-instanton level, including all perturbative fluctuations about the instantons. The result shows a pattern that allows us to determine the asymptotic behaviour of all higher instanton corrections within this solution. We find that the generating function for the leading terms of the latter is given by the Lambert W-function.

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arXiv2010

Free Lunch from T-Duality

We consider a simple method of generating solutions to Einstein gravity coupled to a dilaton and a 2-form gauge potential in n dimensions, starting from an arbitrary (n-m)-dimensional Ricci-flat metric with m commuting Killing vectors. It essentially consists of a particular combination of coordinate transformations and T-duality and is related to the so-called null Melvin twists and TsT transformations. Examples obtained in this way include two charged black strings in five dimensions and a finite action configuration in three dimensions derived from empty flat space. The latter leads us to amend the effective action by a specific boundary term required for it to admit solutions with positive action. An extension of our method involving an S-duality transformation that is applicable to four-dimensional seed metrics produces further nontrivial solutions in five dimensions.

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arXiv2007

Membrane instantons from mirror symmetry

We use mirror symmetry to determine and sum up a class of membrane instanton corrections to the hypermultiplet moduli space metric arising in Calabi-Yau threefold compactifications of type IIA strings. These corrections are mirror to the D1 and D(-1)-brane instantons on the IIB side and are given explicitly in terms of a single function in projective superspace. The corresponding four-dimensional effective action is completely fixed by the Euler number and the genus zero Gopakumar-Vafa invariants of the mirror Calabi-Yau.

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arXiv2007

Orientifolding in N=2 Superspace

We discuss orientifold projections on superspace effective actions for hypermultiplets. We present a simple and new mechanism that allows one to find the Kahler potential and complex structure for the N=1 theory directly in terms of the parent N=2 theory. As an application, we demonstrate our method for Calabi-Yau orientifold compactifications of type IIB superstrings.

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arXiv2006

Fivebrane Instanton Corrections to the Universal Hypermultiplet

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.

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arXiv2005

Masses and Dualities in Extended Freedman-Townsend Models

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 Stueckelberg 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.

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arXiv2005

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.

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arXiv2005

On de Sitter Vacua in Type IIA Orientifold Compactifications

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.

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arXiv2003

Instantons in the Double-Tensor Multiplet

The double-tensor multiplet naturally appears in type IIB superstring compactifications on Calabi-Yau threefolds, and is dual to the universal hypermultiplet. We revisit the calculation of instanton corrections to the low-energy effective action, in the supergravity approximation. We derive a Bogomolny'i bound for the double-tensor multiplet and find new instanton solutions saturating the bound. They are characterized by the topological charges and the asymptotic values of the scalar fields in the double-tensor multiplet.

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arXiv2003

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.

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arXiv2001

Ward Identities for N=2 Rigid and Local Supersymmetry in Euclidean Space

We construct and check by explicit Feynman diagram calculations the BRST Ward identities for N=2 rigid super Yang-Mills theory and N=2 extended supergravity in four-dimensional Euclidean space without auxiliary fields. We use the Batalin-Vilkovisky formalism. In the supergravity case we need one new contractible pair of complex spinor fields to obtain the usual gauge-fixing term and corresponding Nielsen-Kallosh ghosts.

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arXiv2000

Nonlinear Vector-Tensor Multiplets Revisited

We give an off-shell formulation of the N=2 supersymmetric new nonlinear vector-tensor multiplet. Interactions arise in this model as a consequence of gauging the central charge of the supersymmetry algebra, which in contrast to previous models with local central charge is achieved without a coupling to a vector multiplet. Furthermore, we present a new action formula that follows from coupling the N=2 linear multiplet to the vector-tensor multiplet.

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arXiv2000

New N=2 Supersymmetric Vector-Tensor Interaction

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 are given.

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arXiv2000

Exotic Gauge Theories from Tensor Calculus

We construct non-standard interactions between exterior form gauge fields by gauging a particular global symmetry of the Einstein-Maxwell action for such fields. Furthermore we discuss generalizations of such interactions by adding couplings to gravitational Chern-Simons forms and to fields arising through dimensional reduction. The construction uses an appropriate tensor calculus.

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arXiv1999

Supersymmetrization of generalized Freedman-Townsend models

We review briefly generalized Freedman-Townsend models found recently by Henneaux and Knaepen, and provide supersymmetric versions of such models in four dimensions which couple 2-form gauge potentials and ordinary gauge fields in a gauge invariant and supersymmetric manner. The latter models have the unusual feature that, in a WZ gauge, the supersymmetry transformations do not commute with all the gauge transformations.

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arXiv1998

D=4, N=1 Supersymmetric Henneaux-Knaepen Models

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 nonlinear 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.

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