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.Comment: Minor changes, clarification added. Contribution to the proceedings of the 36th International Symposium Ahrenshoop, August 200

Supergravity description of spacetime instantons

We present and discuss BPS instanton solutions that appear in type II string theory compactifications on Calabi-Yau threefolds. From an effective action point of view these arise as finite action solutions of the Euclidean equations of motion in four-dimensional N=2 supergravity coupled to tensor multiplets. As a solution generating technique we make use of the c-map, which produces instanton solutions from either Euclidean black holes or from Taub-NUT like geometries.Comment: 35 pages, some clarifications adde

On NS5-brane instantons and volume stabilization

We study general aspects of NS5-brane instantons in relation to the stabilization of the volume modulus in Calabi-Yau compactifications of type II strings with fluxes, and their orientifold versions. These instantons correct the Kahler potential and generically yield significant contributions to the scalar potential at intermediate values of string coupling constant and volume. Under suitable conditions they yield uplifting terms that allow for meta--stable de Sitter vacua.Comment: 29 pages, 3 figures; statements about fields G^a made more precise, added some clarifications, typos correcte

The Tensor Hierarchies of Pure N=2,d=4,5,6 Supergravities

We study the supersymmetric tensor hierarchy of pure (gauged) N=2,d=4,5,6 supergravity and compare them with those of the pure, ungauged, theories (worked out by Gomis and Roest for d=5) and the predictions of the Kac-Moody approach made by Kleinschmidt and Roest. We find complete agreement in the ungauged case but we also find that, after gauging, new Stueckelberg symmetries reduce the number of independent "physical" top-forms. The analysis has to be performed to all orders in fermion fields. We discuss the construction of the worldvolume effective actions for the p-branes which are charged with respect to the (p+1)-form potentials and the relations between the tensor hierarchies and p-branes upon dimensional reduction.Comment: LaTeX2e file, 20 pages, 1 figure Results refined by extension of the analysis to all orders in fermion

Special Geometry of Euclidean Supersymmetry III: the local r-map, instantons and black holes

We define and study projective special para-Kahler manifolds and show that they appear as target manifolds when reducing five-dimensional vector multiplets coupled to supergravity with respect to time. The dimensional reductions with respect to time and space are carried out in a uniform way using an epsilon-complex notation. We explain the relation of our formalism to other formalisms of special geometry used in the literature. In the second part of the paper we investigate instanton solutions and their dimensional lifting to black holes. We show that the instanton action, which can be defined after dualising axions into tensor fields, agrees with the ADM mass of the corresponding black hole. The relation between actions via Wick rotation, Hodge dualisation and analytic continuation of axions is discussed.Comment: 72 pages, 2 figure

On BPS bounds in D=4 N=2 gauged supergravity II: general matter couplings and black hole masses

We continue the analysis of BPS bounds started in arXiv:1110.2688, extending it to the full class of N=2 gauged supergravity theories with arbitrary vector and hypermultiplets. We derive the general form of the asymptotic charges for asymptotically flat (M_4), anti-de Sitter (AdS_4), and magnetic anti-de Sitter (mAdS_4) spacetimes. Some particular examples from black hole physics are given to explicitly demonstrate how AdS and mAdS masses differ when solutions with non-trivial scalar profiles are considered.Comment: 21 pages; v2 added reference, published version; v3 minor correction

Einstein-Maxwell gravitational instantons and five dimensional solitonic strings

We study various aspects of four dimensional Einstein-Maxwell multicentred gravitational instantons. These are half-BPS Riemannian backgrounds of minimal N=2 supergravity, asymptotic to R^4, R^3 x S^1 or AdS_2 x S^2. Unlike for the Gibbons-Hawking solutions, the topology is not restricted by boundary conditions. We discuss the classical metric on the instanton moduli space. One class of these solutions may be lifted to causal and regular multi `solitonic strings', without horizons, of 4+1 dimensional N=2 supergravity, carrying null momentum.Comment: 1+30 page

Extending trust to immigrants: Generalized trust, cross-group friendship and anti-immigrant sentiments in 21 European societies.

The aim of this study is twofold. First, we expand on the literature by testing whether generalized trust is negatively related to anti-immigrant sentiments in Europe. Second, we examine to what extent the relation between generalized trust and anti-immigrant sentiments is dependent upon cross-group friendships. We apply multilevel linear regression modeling to representative survey data enriched with levels of ethnic diversity covering 21 European countries. Results show that both generalized trust and cross-group friendship are negatively related to anti-immigrant sentiments. However, there is a negligible positive relation between generalized trust and cross-group friendship (r = .10), and we can clearly observe that they operate independently from one another. Hence, trusting actors are not more likely to form more cross-group friendships, and cross-group friendship do not lead to the development of more generalized trust. Instead, the findings show that generalized trust leads immigrants too to be included in the radius of trusted others and, as a consequence, the benign effects of generalized trust apply to them as well. We conclude that the strength of generalized trust is a form of generalization, beyond the confines of individual variations in intergroup experiences

Twistors and Black Holes

Motivated by black hole physics in N=2, D=4 supergravity, we study the geometry of quaternionic-Kahler manifolds M obtained by the c-map construction from projective special Kahler manifolds M_s. Improving on earlier treatments, we compute the Kahler potentials on the twistor space Z and Swann space S in the complex coordinates adapted to the Heisenberg symmetries. The results bear a simple relation to the Hesse potential \Sigma of the special Kahler manifold M_s, and hence to the Bekenstein-Hawking entropy for BPS black holes. We explicitly construct the ``covariant c-map'' and the ``twistor map'', which relate real coordinates on M x CP^1 (resp. M x R^4/Z_2) to complex coordinates on Z (resp. S). As applications, we solve for the general BPS geodesic motion on M, and provide explicit integral formulae for the quaternionic Penrose transform relating elements of H^1(Z,O(-k)) to massless fields on M annihilated by first or second order differential operators. Finally, we compute the exact radial wave function (in the supergravity approximation) for BPS black holes with fixed electric and magnetic charges.Comment: 47 pages, v2: typos corrected, reference added, v3: minor change

Lectures on Gauged Supergravity and Flux Compactifications

The low-energy effective theories describing string compactifications in the presence of fluxes are so-called gauged supergravities: deformations of the standard abelian supergravity theories. The deformation parameters can be identified with the various possible (geometric and non-geometric) flux components. In these lecture notes we review the construction of gauged supergravities in a manifestly duality covariant way and illustrate the construction in several examples.Comment: 48 pages, lectures given at the RTN Winter School on Strings, Supergravity and Gauge Theories, CERN, January 200