Metastable de Sitter vacua in N=2 to N=1 truncated supergravity

We study the possibility of achieving metastable de Sitter vacua in general N=2 to N=1 truncated supergravities without vector multiplets, and compare with the situations arising in N=2 theories with only hypermultiplets and N=1 theories with only chiral multiplets. In N=2 theories based on a quaternionic manifold and a graviphoton gauging, de Sitter vacua are necessarily unstable, as a result of the peculiar properties of the geometry. In N=1 theories based on a Kahler manifold and a superpotential, de Sitter vacua can instead be metastable provided the geometry satisfies some constraint and the superpotential can be freely adjusted. In N=2 to N=1 truncations, the crucial requirement is then that the tachyon of the mother theory be projected out from the daughter theory, so that the original unstable vacuum is projected to a metastable vacuum. We study the circumstances under which this may happen and derive general constraints for metastability on the geometry and the gauging. We then study in full detail the simplest case of quaternionic manifolds of dimension four with at least one isometry, for which there exists a general parametrization, and study two types of truncations defining Kahler submanifolds of dimension two. As an application, we finally discuss the case of the universal hypermultiplet of N=2 superstrings and its truncations to the dilaton chiral multiplet of N=1 superstrings. We argue that de Sitter vacua in such theories are necessarily unstable in weakly coupled situations, while they can in principle be metastable in strongly coupled regimes.Comment: 40 pages, no figure

Axion Stabilization in Type IIB Flux Compactifications

A scenario for stabilization of axionic moduli fields in the context of type IIB Calabi-Yau flux compactifications is discussed in detail. We consider the case of a Calabi-Yau orientifold with h^{1,1}_- \neq 0 which allows for the presence of B_2 and C_2-moduli. In an attempt to generalize the KKLT and the Large Volume Scenario, we show that these axions can also be stabilized - some already at tree level, and others when we include perturbative \alpha'-corrections to the Kaehler potential K and nonperturbative D3-instanton contributions to the superpotential W. At last, we comment on the possible influence of worldsheet instantons on the process of moduli stabilization.Comment: 34 pages, 1 figure; improved referencing, published versio

D-instantons and twistors

Finding the exact, quantum corrected metric on the hypermultiplet moduli space in Type II string compactifications on Calabi-Yau threefolds is an outstanding open problem. We address this issue by relating the quaternionic-Kahler metric on the hypermultiplet moduli space to the complex contact geometry on its twistor space. In this framework, Euclidean D-brane instantons are captured by contact transformations between different patches. We derive those by recasting the previously known A-type D2-instanton corrections in the language of contact geometry, covariantizing the result under electro-magnetic duality, and using mirror symmetry. As a result, we are able to express the effects of all D-instantons in Type II compactifications concisely as a sum of dilogarithm functions. We conclude with some comments on the relation to microscopic degeneracies of four-dimensional BPS black holes and to the wall-crossing formula of Kontsevich and Soibelman, and on the form of the yet unknown NS5-brane instanton contributions.Comment: 47 pages, 1 figure, uses JHEP3.cl

New potentials from Scherk-Schwarz reductions

We study compactifications of eleven-dimensional supergravity on Calabi-Yau threefolds times a circle, with a duality twist along the circle a la Scherk-Schwarz. This leads to four-dimensional {N} = 2 gauged supergravity with a semi-positive definite potential for the scalar fields, which we derive explicitly. Furthermore, inspired by the orientifold projection in string theory, we define a truncation to {N} = 1 supergravity. We determine the D-terms, Kähler-and superpotentials for these models and study the properties of the vacua. Finally, we point out a relation to M-theory compactifications on seven-dimensional manifolds with G 2 structure

Rholography, black holes and Scherk-Schwarz

We present a construction of a class of near-extremal asymptotically flat black hole solutions in four (or five) dimensional gauged supergravity with R-symmetry gaugings obtained from Scherk-Schwarz reductions on a circle. The entropy of these black holes is counted holographically by the well known MSW (or D1/D5) system, with certain twisted boundary conditions labeled by a twist parameter rho. We find that the corresponding (0, 4) (or (4, 4)) superconformal algebras are exactly those studied by Schwimmer and Seiberg, using a twist on the outer automorphism group. The interplay between R-symmetries, rho-algebras and holography leads us to name our construction "Rholography"