Unusual gauged supergravities from type IIA and type IIB orientifolds

We analyse different N=4 supergravities coupled to six vector multiplets corresponding to low-energy descriptions of the bulk sector of T6/Z2 orientifolds with p-brane in IIB (p odd) and in IIA (p even) superstrings. When fluxes are turned on, a gauging emerges corresponding to some non-semisimple Lie algebra related to nilpotent subalgebras Np⊂so(6,6), with dimension hNp=15+(p−3)(9−p). The non-metric axions have Stueckelberg couplings that induce a spontaneous breaking of gauge symmetries. In four cases the gauge algebra is non-Abelian with a non-commutative structure of the compactification torus, due to fluxes of NS–NS and R–R forms.