For G = G(R), a split, simply connected, semisimple Lie group of rank n and K the maximal compact subgroup of G, we give a method for computing Iwasawa coordinates of KG using the Chevalley generators and the Steinberg presentation. When KG is a scalar coset for a supergravity theory in dimensions = 3, we determine the action of the integral form G(Z) on KG. We give explicit results for the action of the discrete U-duality groups SL2(Z) and E-7(Z) on the scalar cosets SO(2)SL2(R) and [SU(8)/{+/- Id}] E7(+7)(R) for type IIB supergravity in ten dimensions and 11-dimensional supergravity reduced to D = 4 dimensions, respectively. For the former, we use this to determine the discrete U-duality transformations on the scalar sector in the Borel gauge and we describe the discrete symmetries of the dyonic charge lattice. We determine the spectrum-generating symmetry group for fundamental BPS solitons of type IIB supergravity in D = 10 dimensions at the classical level and we propose an analog of this symmetry at the quantum level. We indicate how our methods can be used to study the orbits of discrete U-duality groups in general. (C) 2015 AIP Publishing LLC.
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