Maximal supergravity in three dimensions: supergeometry and differential forms

The maximal supergravity theory in three dimensions, which has local SO(16) and rigid E-8 symmetries, is discussed in a superspace setting starting from an off-shell superconformal structure. The on-shell theory is obtained by imposing further constraints. It is essentially a non-linear sigma model that induces a Poincare supergeometry that is described in detail. The possible p-form field strengths, for p = 2, 3, 4, are explicitly constructed using supersymmetry and E-8. The gauged theory is also discussed.