Gauged Supergravities and the Physics of Extra Dimensions

This thesis analyses gauged supergravities in various dimensions and their possible origin from compactifications of string theory. In the effective description the fluxes appear in the theory as deformation parameters generating a potential for the scalar fields. Physics after compactification is only sensitive to the orbits of the global symmetry group, in that gaugings lying in the same orbit are related by duality transformations. Given a certain gauged supergravity containing non-geometric fluxes, we discuss in dimension seven and higher whether there exists a duality transformation that rotates them away and, for those cases in which this is not possible, we give an interpretation as compactifications of Double Field Theory (DFT). Focusing then on our better understanding of geometric flux compactifications, we analyse further in this thesis a class of compactifications down to four dimensions which are compatible with half-maximal supersymmetry (orientifold compactifications) and discuss their embedding in maximal supergravity in the limit of vanishing local sources.