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. † Talk given by S. Vandoren.

General Lagrangians are constructed for N=2 supersymmetric gauge theories in four space-time dimensions involving gauge groups with (non-abelian) electric and magnetic charges. The charges induce a scalar potential, which, when the charges are regarded as spurionic quantities, is invariant under electric/magnetic duality. The resulting theories are especially relevant for supergravity, but details of the extension to local supersymmetry will be discussed elsewhere. The results include the coupling to hypermultiplets. Without the latter, it is demonstrated how an off-shell representation can be constructed based on vector and tensor supermultiplets.

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.