U-duality Twists and Possible Phase Transitions in 2+1D Supergravity

We study 2+1D toroidal compactifications of M-theory with twists in the U-duality group. These compactifications realize many symmetric-manifolds from the classification of 2+1D extended supergravity moduli-spaces. We then focus on the moduli-space $SU(2,1)/U(2)$ obtained by dimensional reduction of pure N=2 supergravity in 3+1D. This space is realized with an explicit example. Assuming that there are no quantum corrections, we conjecture that the classical discrete duality group has to be augmented with an extra strong/weak coupling duality. This implies the existence of new phases of the theory in which the original 8 compactification radii are all fixed at the Planck scale.