Generalized complex geometry of pure backgrounds in ten and eleven dimensions

26 pages. Typos fixed, references addedInternational audiencePure backgrounds are a natural generalization of supersymmetric Calabi-Yau compactifications in the presence of flux. They are described in the language of generalized SU(d) x SU(d) structures and generalized complex geometry, and they exhibit some interesting general patterns: the internal manifold is generalized Calabi-Yau, while the Ramond-Ramond flux is exact in a precise sense discussed in this paper. We have shown that although these two characteristics do persist in the case of generic ten-dimensional Euclidean type II pure backgrounds, they do not capture the full content of supersymmetry. We also discuss the uplift of real Euclidean type IIA pure backgrounds to supersymmetric backgrounds of Lorentzian eleven-dimensional supergravity