On non-geometric fluxes and mixed-symmetry potentials

After a brief discussion of RR and NS fluxes, we consider the T-duality family of fluxes whose prototype is the Scherk-Schwarz reduction of the S-dual of the RR scalar of IIB supergravity. We give a complete classification of these fluxes, including the ones that are non-geometric, and we explain their relation with dual mixed-symmetry potentials. We point out that the non-geometric fluxes turn out to be dual to potentials containing nine antisymmetric indices. Our analysis suggests that all these fluxes can be understood in the context of double field theory, although for the non-geometric ones one expects a violation of the strong constraint.