Abstract:
We find new supersymmetric four-dimensional Minkowski flux vacua of type II string theory on nilmanifolds and solvmanifolds. We extend the results of M. Grana, R. Minasian, M. Petrini, and A. Tomasiello to the case of intermediate SU(2) structures (the two internal supersymmetry parameters are neither parallel nor orthogonal). As pointed out recently by P. Koerber and D. Tsimpis, intermediate SU(2) structures are possible when one considers "mixed" orientifold projection conditions. To find our vacua, we rewrite these projection conditions in a more tractable way by introducing new variables: the projection basis. In these variables, the SUSY conditions become also much simpler to solve, and we find three new vacua. In addition, we find that these variables correspond to the SU(2) structure appearing with the dielectric pure spinors, objects introduced and discussed by R. Minasian, M. Petrini, A. Zaffaroni, and N. Halmagyi, A. Tomasiello, in the AdS/CFT context. Besides, our solutions provide some intuition on what a dynamical SU(3) x SU(3) structure solution could look like.

Abstract:
We study Minkowski supersymmetric flux vacua of type II string theory. Based on the work by M. Grana, R. Minasian, M. Petrini and A. Tomasiello, we briefly explain how to reformulate things in terms of Generalized Complex Geometry, which appears to be a natural framework for these compactifications. In particular, it provides a mathematical characterization of the internal manifold, and one is then able to find new solutions, which cannot be constructed as usual via T-dualities from a warped T^6 solution. Furthermore, we discuss how, thanks to a specific change of variables, one can ease the resolution of the orientifold projection constraints pointed out by P. Koerber and D. Tsimpis. One is then able to find new solutions with intermediate SU(2) structure.

Abstract:
Non-geometry has been introduced when considering a new type of string backgrounds, for which stringy symmetries serve as transition functions between patches of the target space. Then, some terms in the potential of four-dimensional gauged supergravities, generated by so-called non-geometric fluxes, have been argued to find a higher-dimensional origin in these backgrounds, even if a standard compactification on those cannot be made. We present here recent results clarifying the relation between these two settings. Thanks to a field redefinition, we reformulate the NSNS Lagrangian in such a way that the non-geometric fluxes appear in ten dimensions. In addition, if an NSNS field configuration is non-geometric, its reformulation in terms of the new fields can restore a standard geometry. A dimensional reduction is then possible, and leads to the non-geometric terms in the four-dimensional potential. Reformulating similarly doubled field theory, we get a better understanding of the role of the non-geometric fluxes, and rewrite the Lagrangian in a manifestly diffeomorphism-covariant manner. We finally discuss the relevance of the field redefinition and the non-geometric fluxes when studying the non-commutativity of string coordinates.

Abstract:
We obtain new supersymmetric flux vacua of type II supergravities on four-dimensional Minkowski times six-dimensional solvmanifolds. The orientifold O4, O5, O6, O7, or O8-planes and D-branes are localized. All but one vacua are in addition not T-dual to a vacuum on the torus. The corresponding solvmanifolds are proven to be Calabi-Yau, with explicit metrics. Other Ricci flat solvmanifolds are shown to be only K\"ahler.

Abstract:
The (abelian bosonic) heterotic string effective action, equations of motion and Bianchi identity at order alpha prime in ten dimensions, are shown to be equivalent to a higher dimensional action, its derived equations of motion and Bianchi identity. The two actions are the same up to the gauge fields: the latter are absorbed in the higher dimensional fields and geometry. This construction is inspired by heterotic T-duality, which becomes natural in this higher dimensional theory. We also prove the equivalence of the heterotic string supersymmetry conditions with higher dimensional geometric conditions. Finally, some known Kahler and non-Kahler heterotic solutions are shown to be trivially related from this higher dimensional perspective, via a simple exchange of directions. This exchange can be encoded in a heterotic T-duality, and it may also lead to new solutions.

Abstract:
In the first half of the paper, we study in details NS-branes, including the NS5-brane, the Kaluza-Klein monopole and the exotic $5_2^2$- or Q-brane, together with Bianchi identities for NSNS (non)-geometric fluxes. Four-dimensional Bianchi identities are generalized to ten dimensions with non-constant fluxes, and get corrected by a source term in presence of an NS-brane. The latter allows them to reduce to the expected Poisson equation. Without sources, our Bianchi identities are also recovered by squaring a nilpotent $Spin(D,D) \times \mathbb{R}^+$ Dirac operator. Generalized Geometry allows us in addition to express the equations of motion explicitly in terms of fluxes. In the second half, we perform a general analysis of ten-dimensional geometric backgrounds with non-geometric fluxes, in the context of $\beta$-supergravity. We determine a well-defined class of such vacua, that are non-geometric in standard supergravity: they involve $\beta$-transforms, a manifest symmetry of $\beta$-supergravity with isometries. We show as well that these vacua belong to a geometric T-duality orbit.

Abstract:
We present a ten-dimensional theory, named \beta-supergravity, that contains non-geometric fluxes and could uplift some four-dimensional gauged supergravities. Building on earlier work, we study here its NSNS sector, where Q- and R-fluxes are precisely identified. Interestingly, the Q-flux is captured in an analogue of the Levi-Civita spin connection, giving rise to a second curvature scalar. We reproduce the ten-dimensional Lagrangian using the Generalized Geometry formalism; this provides us with enlightening interpretations of the new structures. Then, we derive the equations of motion of our theory, and finally discuss further aspects: the dimensional reduction to four dimensions and comparison to gauged supergravities, the obtention of ten-dimensional purely NSNS solutions, the extensions to other sectors and new objects, the supergravity limit, and eventually the symmetries, in particular the \beta gauge transformation. We also introduce the related notion of a generalized cotangent bundle.

Abstract:
We study ten-dimensional supersymmetric vacua with NSNS non-geometric fluxes, in the framework of $\beta$-supergravity. We first provide expressions for the fermionic supersymmetry variations. Specifying a compactification ansatz to four dimensions, we deduce internal Killing spinor equations. These supersymmetry conditions are then reformulated in terms of pure spinors, similarly to standard supergravity vacua admitting an SU(3)xSU(3) structure in Generalized Complex Geometry. The standard d-H acting on the pure spinors is traded for a generalized Dirac operator D, depending here on the non-geometric fluxes. Rewriting it with an exponential of the bivector $\beta$ leads us to discuss the geometrical characterisation of the vacua in terms of a $\beta$-twist, in analogy to the standard twist by the b-field. Thanks to D, we also propose a general expression for the superpotential to be obtained from standard supergravities or $\beta$-supergravity, and verify its agreement with formulas of the literature. We finally comment on the Ramond-Ramond sector, and discuss a possible relation to intermediate or dynamical SU(2) structure solutions.

Abstract:
It is well known that a constant O(n,n,Z) transformation can relate different string backgrounds with n commuting isometries that have very different geometric and topological properties. Here we construct discrete families of (flux) backgrounds on internal manifolds of different topologies by performing certain coordinate dependent O(d,d) transformations, where d is the dimension of the internal manifold. Our two principal examples include respectively the family of type IIB compactifications with D5 branes and O5 planes on six-dimensional nilmanifolds, and the heterotic torsional backgrounds.

Abstract:
The NSNS Lagrangian of ten-dimensional supergravity is rewritten via a change of field variables inspired by Generalized Complex Geometry. We obtain a new metric and dilaton, together with an antisymmetric bivector field which leads to a ten-dimensional version of the non-geometric Q-flux. Given the involved global aspects of non-geometric situations, we prescribe to use this new Lagrangian, whose associated action is well-defined in some examples investigated here. This allows us to perform a standard dimensional reduction and to recover the usual contribution of the Q-flux to the four-dimensional scalar potential. An extension of this work to include the R-flux is discussed. The paper also contains a brief review on non-geometry.